21:34 - Gathering of Moons
Category: Art and Photography

Gathering of Moons

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A trio of icy moons crowds together along Cassini's line of sight.

Brilliant Enceladus (504 kilometers, 313 miles across) sits on the planet's shadow-draped limb at center; Pandora (81 kilometers, 50 miles across) is a bright speck hovering near the rings; and Mimas (396 kilometers, 246 miles across) is seen at lower right.

This view looks toward the sunlit side of the rings from about a degree below the ringplane.

The image was taken in visible green light with the Cassini spacecraft wide-angle camera on June 28, 2007. The view was obtained at a distance of approximately 291,000 kilometers (181,000 miles) from Enceladus. Scale in the image ranges from 17 kilometers (11 miles) per pixel on Enceladus to 32 kilometers (20 miles) per pixel on Saturn, in the background.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Released: October 1, 2008

source: CICLOPS

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23:04 - Mimas Adrift
Category: Art and Photography

Mimas Adrift

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Cassini looks beyond Saturn's limb toward the icy face of Mimas, the innermost of the planet's major moons.

This view looks toward the sunlit side of the rings from about 3 degrees below the ringplane. Mimas is 396 kilometers (246 miles) across.

Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft narrow-angle camera on Sept. 4, 2007 at a distance of approximately 2.7 million kilometers (1.7 million miles) from Saturn and 2.8 million kilometers (1.8 million miles) from Mimas. Image scale is 16 kilometers (10 miles) per pixel on Saturn and 17 kilometers (11 miles) per pixel on Mimas.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Released: September 26, 2008

source: CICLOPS

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04:52 - How different from Earth are distant exoplanets?
Category: Travel and Places

How different from Earth are distant exoplanets?

Program 5616 of the Earth & Sky Radio Series with hosts Deborah Byrd, Joel Block, Lindsay Patterson and Jorge Salazar.

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Image Credit: NASA / Goddard Space Flight Center

Dave Charbonneau: One of the big delights in the last decade has been that we've uncovered a great diversity in the planets orbiting other stars.

Dave Charbonneau is an astronomer at the Harvard-Smithsonian Center for Astrophysics. He's talking about the discovery so far of over 300 exoplanets – planets that lie beyond our solar system.

Dave Charbonneau: We're getting to the point in terms of studying planets from other stars where we can actually compare different planets to try to understand why they're different, and what causes those differences, i.e. are they made of different stuff, did they form by different process, and are their atmospheres significantly different.

Chabonneau's observed the light an exoplanet emits as it passes by its parent star, to actually see what gases are in the atmospheres of those distant worlds, light-years away. Ultimately what Charbonneau searches for, and no human has yet found, is a distant planet like Earth with a life-giving atmosphere.

Dave Charbonneau: I think that we will soon have, for the first time in human history, the sensitivity to actually find one. I think everyone regardless of whether they're a scientist or not, has wondered about the Earth's place in the universe and about the possibility of life on other planets. And by looking for and finding analogues of the Earth, this is really our first step to address that question.

source: Earth & Sky Radio Series

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15:00 - White Moon
Category: Art and Photography

White Moon

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As Cassini sped away from Enceladus following its close Aug. 2008 flyby, the moon's wrinkled south polar region remained in view.

The blue-green hues so apparent in false color views like PIA11112 (obtained three hours before this image) are absent in natural-color views like this one, which approximate the scene as it might appear to human eyes. In visible light, the surface of Enceladus is almost perfectly white.

Images taken using red, green and blue spectral filters were combined to create this view. The images were digitally reprojected onto a computer model of Enceladus, and aligned there, in order to account for the spacecraft's rapid motion with respect to the moon.

The images were acquired with the Cassini spacecraft narrow-angle camera on Aug. 12, 2008 at a distance of approximately 201,000 kilometers (125,000 miles) from Enceladus. Image scale is 1 kilometer (0.6 mile) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Released: September 19, 2008

source: CICLOPS

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13:54 - How windy is it on Venus? Venus Express answers
Category: Travel and Places

How windy is it on Venus? Venus Express answers

It is well known that winds on Venus are extremely fast and powerful. Now, ESA's Venus Express has, for the first time, put together a 3-D picture of the venusian winds for an entire planetary hemisphere.

The most powerful atmospheric investigator ever sent to Venus, Venus Express has an advantageous orbit around the planet and a unique set of instruments. The spacecraft has the ability to peer through Venus's thick atmospheric layers and obtain a truly global picture.

This animation of wind circulation on Venus is composed of images taken by the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA's Venus Express between April 2006 and June 2007.

VIRTIS observations have provided the first-ever 3-D picture of the venusian winds for an entire planetary hemisphere. Images of the night-side (the red part of the globe) were obtained at the infrared wavelength of 1.74 micrometres, which allows tracking of the clouds at the lower boundary of the cloud layer (about 45-47 km altitude). The day-side images (the grey part of the globe) were obtained both in the near-infrared at about 980 nanometres (a window to the clouds at about 61 km altitude), and in the blue ultraviolet at about 350 nanometres (about 66 km altitude).

The non-annotated version of this animation is downloadable here.

Credits: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/ Universidad del País Vasco (R.Hueso)

The spacecraft has continuously monitored the planet since observations began in 2006, and scientists now have enough data to start building a complete picture of the planet's atmospheric phenomena.

The Venus Express Visual and Infrared Thermal Imaging Spectrometer, VIRTIS, has been studying the thick blanket of clouds that surround Venus, gathering data on the winds. The area studied spans altitudes of 45 to 70 km above the surface and covers the entire southern hemisphere, up to the equator. It is above the southern hemisphere that Venus Express reaches its highest point in orbit (about 66 000 km), allowing the instruments to obtain a global view.

Agustin Sánchez-Lavega, from the Universidad del País Vasco in Bilbao, Spain, led the research on 3-D wind mapping with data from the first year of VIRTIS observations. "We focused on the clouds and their movement. Tracking them for long periods of time gives us a precise idea of the speed of the winds that make the clouds move and of the variation in the winds," he said.

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The different atmospheric layers and respective wind speeds between the equator and 50-55° latitude on the southern hemisphere of Venus, as measured by the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA's Venus Express between April 2006 and June 2007.

Using three different wavelengths as windows to three different atmospheric layers, VIRTIS tracked the movement of clouds and determined the speed of the winds moving them. The instrument has provided the first-ever 3-D picture of the venusian winds for an entire planetary hemisphere.

Observing at the infrared wavelength of 1.74 micrometres on the night-side of the planet, VIRTIS can see down to 45-47 km altitude; the clouds at this altitude can be seen because they absorb infrared light coming from the surface and the lower atmospheric layers, and this light is then re-emitted by the clouds themselves. At this height, the average wind speed is about 210 km/h.

Observing in the near-infrared (about 980 nanometres) and in the blue ultraviolet (about 350 nanometres) on the day-side of the planet, VIRTIS can look down to about 61 and 66 km altitude (the higher part of the cloud layer), respectively. Sunlight reflected by the clouds at the two different layers in the infrared and in the ultraviolet makes it possible to track them. The measured wind speeds are 220 and 370 km/h, respectively.

Credits: R. Hueso (Universidad del País Vasco)

Tracking the clouds at different altitudes is possible only if the instrument is able to look through the curtain of clouds. "VIRTIS operates at different wavelengths, each of which penetrates the cloud layer to a different altitude," added Ricardo Hueso, also from the Universidad del País Vasco, co-author of the results. "We studied three atmospheric layers and followed the movement of hundreds of clouds in each. This has never been done before at such large temporal and spatial scales, and with multi-wavelength coverage."

In total, the team tracked 625 clouds at about 66 km altitude, 662 at around 61 km altitude, and 932 at about 45-47 km altitude, on the day and night sides of the planet. The individual cloud layers were imaged over several months for about 1-2 hours each time.

"We have learnt that between the equator and 50-55° latitude south, the speed of the winds varies a lot, from about 370 km/h at a height of 66 km down to about 210 km/h at 45-47 km", said Sánchez-Lavega.

"At latitudes higher than 65°, the situation changes dramatically - the huge hurricane-like vortex structure present over the poles takes over. All cloud levels are pushed on average by winds of the same speed, independently of the height, and their speed drops to almost zero at the centre of the vortex."

Sánchez-Lavega and colleagues observed that the speed of the zonal winds (which blow parallel to the lines of latitude) strongly depend on the local time. The difference in the Sun's heat reaching Venus in the mornings and in the evenings - called the solar tide effect - influences the atmospheric dynamics greatly, making winds blow more strongly in the evenings.

On average, the winds regain their original speeds every five days, but the mechanism that produces this periodicity needs further investigation. "VIRTIS is continuing its observations, and over the next few years we expect to understand more precisely how stable or variable the venusian winds at the upper and lower cloud layers are," concluded Giuseppe Piccioni, from the Istituto Nazionale di Astrofisica in Rome, Italy, co-Principal Investigator for the VIRTIS instrument.

Notes for editors:

The results appear in the 10 July issue of the Geophysical Research Letters journal, in the article 'Variable winds on Venus mapped in three dimensions', by A. Sánchez-Lavega, R.Hueso, J.Peralta, S.Pérez-Hoyos (Universidad del País Vasco in Bilbao, Spain), G.Piccioni (Ist. Nazionale di Astrofisica and Ist. Di Astrofisica Spaziale e Fisica Cosmica, Rome, Italy), P.Drossart and S.Erard (Observatoire de Paris/LESIA, France), C.F.Wilson and F.W.Taylor (University of Oxford, UK), K.H.Baines (NASA/JPL, Pasadena, CA, USA), D.Luz (Observatoire de Paris/LESIA, France, and Observatório Astronómico de Lisboa, Portugal), S.Lebonnois (CNRS/UPMC, Paris, France).

source: ESA Space Science

A three-dimensional view of variable winds in the cloud layers on Venus

A detailed, three-dimensional view of the wind speeds and directions in the cloud layers of Venus has been obtained with the VIRTIS instrument on Venus Express. This study, which benefited from an extensive and homogeneous data set, contributes to a better understanding of the temporal and spatial behaviour of the winds on Venus.

A team of astronomers, led by Agustin Sánchez-Lavega from Universidad del Pais Vasco, has used spectral images recorded with VIRTIS between April 2006 and June 2007 to track and study cloud features over the entire southern hemisphere of Venus. These clouds probe the winds in the thick cloud and haze layers that encircle the entire planet at altitudes between 30 and 70 km.

The study was performed by examining cloud features in pairs of images taken between 20 and 74 minutes apart. The evolution of the cloud features between each image provided a measure of their location as a function of time. From this the zonal and meridional wind speeds were derived.

Figure 1. Composite VIRTIS view of Venus's day side (grey) and night side (red). Credit: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/ Universidad del País Vasco (R. Hueso)

Multi-wavelength spectral images from VIRTIS can be used to probe different altitudes in the thick cloud layers of Venus. In their study, Sánchez-Lavega and colleagues probed three different altitude ranges using the three wavelengths: 0.38 µm, 0.98 µm and 1.74 µm (see Table 1).

Table 1. Characteristics of the data used in this study

Observed wind speeds

Figure 2 shows the mean wind speed as a function of latitude for both the zonal wind and meridional wind as derived from the observed cloud features. The values are temporally and spatially averaged over narrow latitude bins. Each plot shows the wind speed variation at the three different altitude ranges: 62-70 km (blue), 58-64 km (purple) and 44-48 km (red).

Date: 18 Sep 2008
Satellite: Venus Express
Depicts: Wind speeds at three altitudes based on VIRTIS data
Copyright: A. Sánchez-Lavega et al. 2008

These two graphs show the averaged wind speeds in the southern hemisphere of Venus as a function of latitude for both the zonal winds, U (A, left) and meridional winds, V (B, right). The spatial and temporal averages of the wind speeds are derived from VIRTIS data recorded between April 2006 (arrival of Venus Express at Venus) and July 2007.

The three curves in each graph show the wind speed in three different altitude ranges in the cloud layers. These were derived by tracking the movement of cloud features at three different wavelengths:

Error bars for the 0.98 µm profile are not drawn for clarity but are similar to the other profiles.

Spatial variations

Clearly visible is the fast westward zonal rotation (known as super-rotation) of the upper cloud deck with an average speed of 102 ms^-1 between 0° and ~55° southern latitude. In the other two altitude ranges the same westward wind is present, but with a substantially lower wind speed (table 2). This implies there is a large shear between adjacent altitude layers mainly in the upper cloud deck and from the equator down to ~55°S.

Table 2. Mean zonal wind speed, temporally and spatially averaged between 0° - 55°S latitude.

At higher southern latitudes the zonal wind speeds drop linearly and steadily toward the pole for all three altitudes. In addition, at these latitudes the difference between the wind speeds in the three altitude ranges diminishes as all layers start to co-rotate coherently with the large polar vortex.

The meridional wind speed was found to vary little with latitude. Taking account of the measurement uncertainties it is only at the top of the upper cloud deck that a trend is observed with an increase from ~0 to ~10 ms^-1, peaking at the latitude 55°S (Figure 2B, blue curve).

Temporal variations

The long time span covered by the observations allowed the team to investigate the temporal variation of the measured wind speed. There was some indication of variation in the speed of the zonal wind as a function of latitude and in the 58-64 km altitude range. It was ~13 ms^-1 faster at the start of observations (in April 2006) compared to the average over the entire observation period. This variation, however, needs to be confirmed with further measurements.

A more pronounced effect found in the course of the study by Sánchez-Lavega and colleagues was a strong dependency on wind speeds with local solar time. Between the morning and mid-afternoon the zonal wind speed increased by about 10 ms^-1. This effect only occurred in the top cloud layers and only at the higher latitudes (above 50°S).

Overall, the results reported in Sánchez-Lavega et al, when combined with measurements of the Venusian wind speeds obtained with other spacecraft, confirm a sharp change in the zonal circulation at ~55 degrees latitude.

Ongoing observations with Venus Express will help to determine if the observed mean wind speeds are stable and typical for Venus, and will further characterise the nature and variations of the mean zonal winds in the cloud layers.

Related publication

Sánchez-Lavega, A., et al. (2008), Variable winds on Venus mapped in three dimensions, Geophys. Res. Lett., 35, L13204, doi:10.1029/2008GL033817

source: ESA: Science and Technology

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06:29 - Fifth Dwarf Planet Named by the IAU
Category: Travel and Places

Fifth Dwarf Planet Named by the IAU

The name Haumea has been approved for the object previously known as 2003 EL61. There are now five objects in the Solar System classified as dwarf planets: Ceres, Pluto, Haumea, Eris, and Makemake.

Haumea's two moons have also been given new names. Hi'iaka (Haumea I) and Namaka (Haumea II) are both daughters of Haumea in Hawaiian mythology.

For more information, see the IAU announcement and the Planet and Satellite Names and Discoverers page in the Gazetteer of Planetary Nomenclature.

source: USGS Astrogeology Hot Topics

Haumea

On December 28th, 2004, I discovered a Kuiper belt object brighter than anything anyone had ever seen before. Being only a few days after Christmas, I naturally nicknamed it Santa.

The discovery was bittersweet. I had made a bet with a friend 5 years earlier that someone – anyone! – would discover a new planet by January 1st, 2005. The deadline was in 3 days, but I knew that Santa didn't count. We didn't know exactly how to define "planet" back then, but we decided that something of a particular brightness would count. Santa was bright , but not quite bright enough. Three days later I had still not found anything bright enough to count, and I lost the bet.

But, still: Santa! How would I have known back in 2004 that Santa would be the single most interesting object ever discovered in the Kuiper belt? It has a moon – wait, no, two moons! It is oblong, sort of like a football (American style) that has been deflated and stepped on. And it rotates end over end every 4 hours, significantly faster than anything else large known anywhere in the solar system.

Large? Well, at least sort of large. The long axis is about the same size as Pluto or Eris or Makemake. Back when I thought that maybe the IAU was going to vote that anything the size of Pluto or larger was a planet I was going to argue that Santa was indeed a planet – as long as you looked at it at exactly the right angle (luckily, the IAU was much more sensible, so I did not have to make such a crazy argument).

Stranger still, Santa has the density of a rock. We think that most things out in the Kuiper belt are about equal portions of rock and of ice, but, apparently, this does not apply to not Santa. It's only rock. Except that even that is not true. When we finally got a chance to look closely at its surface with the Keck telescope we realized that the surface is nothing but ice. Santa must have a structure like an M&M, except that instead of a thin layer of sugar surrounding chocolate, the thin outer shell is ice and the interior is rock. Don't bite.

These characteristics already make Santa the strangest object in the Kuiper belt. Several years ago we came up with what thought was a good explanation. What if, eons ago, Santa was an even larger Kuiper belt object and it got smacked – in a glancing blow – by another Kuiper belt object? That would explain the fast spin. And the fast spin would be enough to explain the oblong shape; anything spinning that fast would be pulled into such a big stretch.

What's more, the initially large Santa could have had a rocky interior and icy exterior, much like the Earth has an iron interior and a rocky interior. When the huge impact occurred, it could have cracked that outer icy mantle and ejected all of that ice into space. The two moons that circle Santa are pieces of that icy mantle.

This explanation was, we thought, pretty good. And then it got really good.

While looking across the Kuiper belt at many different objects, we realized that a small number of objects in the Kuiper belt look like tiny little chunks of ice. How strange. Even stranger, though, was that all of these chunks of ice were, relatively speaking, next-door neighbors of Santa. We had found the other chunks that had been removed from the mantle of Santa. The story was complete.

……………………………….

After we discovered Santa, we worked hard to get the first scientific paper ready to announce the discovery. In science there is always a tension between doing the careful work to make a complete announcement and doing an instant but incomplete announcement in order to make sure you don't get scooped. We were as worried as anyone about being scooped, but we resisted the temptation for instant announcement. We felt that the science was too important.

On July 7th 2005, as I was putting the finishing touches on the scientific paper, in hopes of submitting it the next day, I had a minor delay. My daughter was born. I had somehow convinced myself that there was no way that she would be born for another week. I was certain that I had more time. But I had no more time, no more time at all. I forgot about Santa and the rest of the Kuiper belt and turned my obsession from it to her. The announcement about Santa would have to wait, I was too busy sending out announcements about Lilah, instead. What difference would a few months make, really?

…………………………………

The announcement did indeed wait, but only for 21 more days. On a late Thursday night, between changing diapers and filling bottles and descending ever more into sleep deprivation, I checked my email and saw the announcement of the discover of Santa myself. A previously unheard-of Spanish team had just discovered Santa a few days earlier. And they called it the tenth planet.

No no no no no no no no! I was horrified. My discovery had just been scooped by a group who decided not to wait to learn more. They didn't know any of the information about Santa that we did, in particular that it has a satellite and from the orbit of the satellite you could tell that it was only 1/3 the size of Pluto, and that it was definitely not the tenth planet. Worse, a few months earlier, we had actually discovered something that was bigger than Pluto. This was going to cause nothing but confusion.

That night, on no sleep but much caffeine, I stayed up to finish the paper about Santa that I had put aside three weeks earlier. We would not get credit for discovery, which was painful enough, but at least we would quickly set the record straight about its size and importance. After I sent the paper off, I sent a quick email to congratulate the Spanish team on their discovery and I filled them in on everything that we knew so that they could answer questions from the press correctly. Finally I nodded off to sleep.

I woke to a nightmare. In the intervening hours it appeared that someone had used the knowledge that we had been tracking Santa to start looking into what else we had been doing. Someone had traced where we had been pointing our telescopes for the past months. We had been pointing them at the object that would one day be called Eris – the object bigger than Pluto, the real tenth planet! That morning, the astronomical coordinates of Eris were posted to a public web page with discussions about what might be there that we had been watching. It was clear to me that as soon as the sun went down that night, anyone with a moderately large amateur telescope could point up in the sky at those coordinates and, the next day, claim they had discovered the 10th planet.

After breakfast, I apologized to my wife; I would have to go in to work today for the first time in three weeks.

I called my wife later in the day to apologize again. I was going to have an international press conference that afternoon and would she mind bringing me some nicer clothes? And a razor, perhaps? And more coffee. Definitely more coffee. That evening, the world learned that there were 10 planets.

……………………………………

After more than three years, Santa received a formal name today. Santa is now, and forever, officially Haumea. From the official citation issued by the International Astronomical Union:

Haumea is the goddess of childbirth and fertility in Hawaiian mythology. Her many children sprang from different parts of her body. She takes many different forms and has experienced many different rebirths. As the goddess of the earth, she represents the element of stone.

The name was chosen by David Rabinowitz of Yale University, one of the co-discoverers of Santa (along with me and Chad Trujillo of Gemini Observatory in Hawaii). He chose the name because Haumea is closely associated with stone, and Santa (as we knew it at the time) appeared to be made of nothing but rock.

But the name is even better than that. Just like the Kuiper belt object Haumea is the central object in a cloud of Kuiper belt objects that are the pieces of it, the goddess Haumea is the mother of many other deities in Hawaiian mythology who are pieces pulled off of her body.

Two of these pieces are Hi'iaka, the patron goddess of the big island of Hawaii, who was born from the mouth of Haumea, and Namaka, a water spirit, who was born from the body of Haumea. These names were chosen for the brighter outer moon and the fainter inner moon, respectively.

Officially:

Haumea I, Hi'iaka, discovered 2005 Jan 26 by M.E. Brown, A.H. Bouchez, and the Keck Observatory Adaptive Optics team

Hi'iaka was born from the mouth of Haumea and carried by her sister Pele in egg form from their distant home to Hawaii. She danced the first Hula on the shores of Puna and is the patron goddess of the island of Hawaii and of hula dancers.

Haumea II, Namaka, discovered 2005 Nov 7 by M.E. Brown, A.H. Bouchez, and the Keck Observatory Adaptive Optics teams

Namaka is a water spirit in Hawaiian mythology. She was born from the body of Haumea and is the sister of Pele. When Pele sends her burning lava into the sea, Namaka cools the lava to become new land.

But wait! Shouldn't the official discoverer get to name the object? What of the Spanish team?

Yes. The discoverer should.

Several weeks after the Spanish team announced the discovery of Santa which precipitated the announcement of the object that would eventually be named Eris, which precipitated the entire discussion of dwarf planets, it became clear that the Spanish team had not been forthcoming. They themselves had been the first to access the web sites which told where our telescopes looked. And they did this access two days before they claimed discover (you can see a detailed timeline reconstructed from the web logs here).

Did they use this information to claim the discovery for themselves?

As a scientist, my job is to examine the evidence and come up with the most plausible story. Here are some possibilities. It is impossible to disprove this story, claimed by the Spanish team: while looking through two-year-old data, they discovered Santa legitimately, and then, only hours later, accessed information about where our telescopes had been looking and were shocked (shocked!) to realize that the object they had just found was the same object that we had been tracking for months. Wanting to establish priority, they quickly announced, knowing essentially nothing about the object.

Though this story cannot be disproved, it does not have much of an air of plausibility about it. Data that were two years old happened to get analyzed just hours before – whoops! – the team found out that someone else had found the same thing? Hmmmmm. Perhaps most damning, you would think that perhaps the Spanish team would be willing to admit this early on. Instead they appeared to attempt to hide the fact that they ever knew anything about our telescope pointings.

Let's try a more plausible explanation: the Spanish team found our telescope pointings, used that information to infer the existence of Santa, and assumed that no one would ever know they had not found it legitimately.

No way to prove it, but the later hypothesis certainly sounds more plausible. To be fair, though, I don't think there is any way to ever know the full extent of the truth, except on the off chance that someone on the Spanish team eventually spills the beans about what really happened. I keep waiting, but I don't hold my breath.

But wait, there's more to ask! If the telescope pointings were – even if inadvertently – on a publicly accessible web site, was it wrong to look at them? The obvious answer is that there is nothing wrong with looking at information on any publicly accessible web site, just as there is nothing wrong with looking at books in a library. But the standards of scientific ethics are also clear: any information used from another source must be acknowledged and cited. One is not allowed to go to a library, find out about a discovery in a book, and then claim that discovery as your own with no mention of having read it in a book. One is not even allowed to first make a discovery and then go to the library and realize that someone else independently made the same discovery and then not acknowledge what you learned in the library. Such actions would be considered scientifically dishonesty.

In the end, while we are likely to never know exactly what happened, it appears clear that the Spanish team was either dishonest or fraudulent. They have claimed the facts that merely make them dishonest. If I had to bet, though, I would bet for the later.

…………………………………………….

Officially, the naming of Haumea does nothing to put to rest this three-year-old controversy. The committee that voted to accept the name has said that, while they will take the name proposed by our team rather than the name proposed by the Spanish team, they are not favoring one claim over the other. They will let posterity decide.

OK, posterity, have at it. If I am no longer around to hear the news on the decision, that's ok, you can tell my daughter Lilah instead. She will have been waiting, nearly precisely, her entire life.

source: Mike Brown's Planets

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06:20 - Approaching Enceladus
Category: Art and Photography

Approaching Enceladus

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As Cassini began its Aug. 2008 flyby of Enceladus, the spacecraft approached over the moon's cratered north pole. Cassini acquired this view as the icy moon grew ever larger in its field of view.

In addition to the sunlit crescent at upper right, the faint glow at bottom indicates a secondary source of illumination: reflected sunlight from Saturn.

The view looks toward high northern latitudes on Enceladus (504 kilometers, 313 miles across) from a perspective 71 degrees north of the moon's equator. The north pole is in shadow at center.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 11, 2008. The view was obtained at a distance of approximately 448,000 kilometers (278,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 113 degrees. Image scale is 3 kilometers (2 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Released: September 17, 2008

source: CICLOPS

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05:20 - Evidence for Planets in Protoplanetary Disk
Category: Travel and Places

Evidence for Planets in Protoplanetary Disks

Using a near-infrared spectrograph attached to ESO's Very Large Telescope, astronomers have been able to examine the inner protoplanetary disks around three interesting stars, with results showing the sheer diversity of the apparently emerging systems. Only a few million years old, all three stars could be considered analogs of our own Sun, going through processes like those that produced the Solar System some 4.6 billion years ago. The disks under study show regions where the dust has been cleared out, the possible signature of planetary influence.

The new work, which offers higher resolution than was earlier available, demonstrates that the previously known gaps in the dust still contain molecular gas, an indication that the dust has begun to form planetary embryos or that a planet has already formed and is clearing the disk gas as it orbits. The likely planets include a massive gas giant orbiting the star SR 21 at a distance of something less than 3.5 AU, and a possible planet around HD 135344B between 10 and 20 AU. The third star, TW Hydrae, may also show the development of one and possibly two planets. In the words of Klaus Pontoppidan (Caltech):

"Our observations with the CRIRES instrument on ESO's Very Large Telescope clearly reveal that the disks around these three young, Sun-like stars are all very different and will most likely result in very different planetary systems."

Image: Astronomers have been able to study planet-forming disks around young Sun-like stars in unsurpassed detail, using ESO's Very Large Telescope. The studied disks were known to have gaps (represented by the brownish color in the image) but the astronomers found that gas is still present inside these gaps (represented by the white color in the image). This can either mean that the dust has clumped together to form planetary embryos, or that a planet has already formed and is in the process of clearing the gas in the disk. Credit: European Southern Observatory.

The techniques on display here, collectively called 'spectro-astrometric imaging,' are dazzling, allowing the researchers to see into the inner disk regions around stars that are more than 200 light years away, measuring distances down to one-tenth of an AU while simultaneously measuring the velocity of the gas. The disks themselves are about 100 AU across. Chalk up yet another win for adaptive optics, as the CRIRES spectrograph is fed by an AO module that corrects for atmospheric blurring, allowing high resolution. As good as these results are, they'll be surpassed not many years from now by the ALMA (Atacama Large Millimeter/submillimeter) Array, whose operations commence in 2012.

Addendum: Andy has passed along the link to the paper on this work, which is Pontoppidan et al., "Spectro-astrometric imaging of molecular gas within protoplanetary disk gaps," accepted for publication in the Astrophysical Journal. The original ESO news release is here.

source: Centauri Dreams

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05:13 - MESSENGER Finalizes Plans for Its Second Look at Mercury
Category: Travel and Places

MESSENGER Finalizes Plans for Its Second Look at Mercury

It is now only slightly more than three weeks before the MESSENGER spacecraft flies by Mercury for the second time. At 4:40 a.m. ET on October 6, the craft will speed by the planet, passing within 125 miles (200 kilometers) and gaining a gravity assist that will tighten its orbit and keep it on its course to pass the planet one last time next year before becoming the first spacecraft ever to orbit Mercury, beginning in 2011.

A comprehensive set of observations of Mercury and its environment has been designed for this upcoming encounter - deploying all seven of the science payload instruments, in addition to the telecommunications system - to continue the investigations begun during the first encounter with Mercury last January.

Over the last six months, engineers have been building the software commands needed to implement these observations into one single sequence that will be loaded to the spacecraft to run automatically during the encounter. The development of this sequence included several levels of review and testing as it matured. Today, engineers successfully completed the final testing of the commands on the hardware simulator, and on September 29, engineers will send MESSENGER instructions on what observations to perform at each point along the flyby trajectory.

As MESSENGER flew by Mercury on January 14, its instruments imaged 20% of Mercury's surface not previously seen by spacecraft. The spacecraft made measurements of the planet's magnetic field, exosphere and sodium tail, surface color and composition, and gravitational field. On its second visit, MESSENGER will image an additional 30% of the surface never before seen by spacecraft.

"MESSENGER's first flyby of Mercury produced many surprises," offered MESSENGER Principal Investigator Sean Solomon. "The second flyby will bring us close to the opposite side of the planet from the one we visited in January, and the surface we will view at close range for the first time is larger in area than South America. The only safe prediction at this stage of exploring the innermost planet is that we will make new discoveries."

Mercury -- in 3D!

This graphic shows a portion of the fault scarp Beagle Rupes cutting through the highly elliptical crater Sveinsdottir in a three-dimensional (3D) representation. Standard 3D glasses (which can be assembled at home), with a red filter in front of the left eye and a blue filter in front of the right one, can be used to view this picture. By combining information from multiple images of the same portion of Mercury's surface taken under different viewing angles, the topography of the surface was determined. A high-resolution image was then overlaid on the topography map, resulting in this 3D image.

More than 80 MESSENGER images were used to create this 3D view of Mercury's surface. As the MESSENGER mission continues, many more images will be acquired, and these additional images will provide views of Mercury's surface from a variety of illumination conditions and viewing geometries. These myriad views, anchored by topographic profiles to be acquired by MESSENGER's laser altimeter, will enable large portions of the surface of Mercury to be studied in 3D.

Stat Corner

MESSENGER is about 51.8 million miles (83.4 million kilometers) from the Sun and 81.5 million miles (131.2 million kilometers) from Earth. At that distance, a signal from Earth reaches the spacecraft in 7.3 minutes. The spacecraft is moving around the Sun at 84,744.7 miles (136,383.4 kilometers) per hour.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and after flybys of Earth, Venus, and Mercury will start a yearlong study of its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

source: Solar System Exploration

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05:05 - First Picture of Likely Planet Around a Sun-Like Star
Category: Life

First Picture of Likely Planet Around a Sun-Like Star

Written by Nancy Atkinson

Astronomers have unveiled what is likely the first picture of a planet around a normal star similar to the Sun. Using the Gemini North telescope on Mauna Kea in Hawaii, astronomers from the University of Toronto imaged the young star 1RXS J160929.1-210524, which lies about 500 light-years from Earth and a candidate companion of that star. They also obtained spectra to confirm the nature of the companion, which has a mass about eight times that of Jupiter, and lies roughly 330 times the Earth-Sun distance away from its star. For comparison, the most distant planet in our solar system, Neptune, orbits the Sun at only about 30 times the Earth-Sun distance. The parent star is similar in mass to the Sun, but is much younger. "This is the first time we have directly seen a planetary mass object in a likely orbit around a star like our Sun," said David Lafrenière, lead author of a paper detailing the discovery. "If we confirm that this object is indeed gravitationally tied to the star, it will be a major step forward."

Until now, the only planet-like bodies that have been directly imaged outside of the solar system are either free-floating in space (i.e. not found around a star), or orbit brown dwarfs, which are dim and make it easier to detect planetary-mass companions.

The existence of a planetary-mass companion so far from its parent star comes as a surprise, and poses a challenge to theoretical models of star and planet formation. "This discovery is yet another reminder of the truly remarkable diversity of worlds out there, and it's a strong hint that nature may have more than one mechanism for producing planetary mass companions to normal stars," said team member Ray Jayawardhana.

The team's Gemini observations took advantage of adaptive optics technology to dramatically reduce distortions caused by turbulence in Earth's atmosphere. The near-infrared images and spectra of the suspected planetary object indicate that it is too cool to be a star or even a more massive brown dwarf, and that it is young.

While it could be a chance alignment between the object and the young star, it will take up to two years to verify that the star and its likely planet are moving through space together. "Of course it would be premature to say that the object is definitely orbiting this star, but the evidence is extremely compelling. This will be a very intensely studied object for the next few years!" said Lafrenière.

Team member Marten van Kerkwijk described the group's search method. "We targeted young stars so that any planetary mass object they hosted would not have had time to cool, and thus would still be relatively bright," he said. "This is one reason we were able to see it at all."

The Jupiter-sized body has an estimated temperature of about 1800 Kelvin (about 1500ºC), much hotter than our own Jupiter, which has a temperature of about 160 Kelvin (-110ºC), and its likely host is a young star of type K7 with an estimated mass of about 85% that of the Sun.

"This discovery certainly has us looking forward to what other surprises nature has in stock for us," said Van Kerkwijk.

Read the team's paper here.

source: Universe Today

PLANET IMAGED AROUND A SUNLIKE STAR?!

Is this it? Is this the very first image of a planet orbiting a star like the Sun?

The image come from the monster 8 meter Gemini North telescope in Hawaii. The star is 1RSX J160929.1-210524 (for those taking notes at home) — it's a K7 dwarf, a bit cooler and smaller than the Sun — and the planet is the blip circled at the upper left. It has no real name as yet —  it hasn't been confirmed yet; more on that in a sec — but if it's a planet orbiting the star, it has a mass of about 8 times that of Jupiter.

The image is in near-infrared, just outside the human range of vision. This is a good place to hunt for young planets, because for millions of years after they are formed, planets are hot and glow in the infrared, while stars like the Sun are faint in the IR. Well, relatively faint; they still pour out energy, but it's a lot less than in the visible part of the spectrum. So using IR detectors means you're looking where young planets put out most of their light, and stars put out the least.

The planet seen by Gemini appears to be about 5 million years old– the parent star is part of a cluster of stars whose age is known. They lie about 500 light years from Earth.

Spectra of the star and planet. Click to embiggen.

The reason astronomers think this is a planet is because they took spectra: they broke the light up into a rainbow, if you will, and when you carefully examine the spectrum you can determine all sorts of things about the object emitting the light: how hot it is, what chemical composition it has, how old it is, even if it's spinning!

The spectrum of the object matches that of an old, very low mass star. That might make you think it's a star, but wait! The planet is young, and still hot. The light it gives off depends on its temperature, so a young low mass object, like a planet, can look just like a more massive object like a star. Since we know this object is young, we know it has a lower mass than its spectrum naively suggests. When models of how planets cool are used, we get a pretty good match for one with 8 times Jupiter's mass if it's the age of the star cluster, 5 million years.

But this is not confirmed! For example, it could be a low mass star that happens to be near the other star along our line-of-sight — in other words, it's in the background. The best way to see if that's true is to wait a year or two and take more images. If the object moves against the background stars along with the brighter star, then it must be physically associated with the star, and therefore it's a planet. This is how we confirmed the first image of an exoplanet back in 2005— but that was orbiting a brown dwarf, a star very different than the Sun.

If confirmed, this one is pretty important, because the parent star is much like our own Sun. The most interesting thing about this is the distance of the purported planet from the star: 50 billion kilometers! That's 11 times the distance Neptune is from the Sun. And that's a lower limit; it might be farther. That makes me very suspicious: we don't know of any way to form planets that far from their parent stars.

Stars and planets form from rotating disks of gas and dust. The stuff collects in the middle to form the star, and the stuff farther out forms the planets — we have seen many examples of this in the sky. The disks we see around new stars are big, sure, but by the time you get 50 billion km out they are very thin, and there's just not enough material out there to form a planet, let alone one with 8 times the mass of Jupiter.

In this case, the most likely explanations for this image are that 1) this isn't a planet, but a background star, or 2) it formed closer in and was ejected by an encounter with another planet, moving it way the heck out from the star. (1) is a bummer, and is unlikely just due to statistics; it's isn't high odds to see an object like this by coincidence so near another star. (2) seems unlikely to me as well; it's hard to toss around a planet that mass unless an even more massive planet was involved. I hope this star is a target for searches for more planets, just to get more information on this scenario.

To their credit, the astronomers involved are also clear about this in their paper announcing the discovery. This is a carefully done observations, and they are appropriately careful in their announcement.

But if it's true… WOW. This would be the second planet ever seen directly in an image, and the first to orbit a star like the Sun. The implications would profound. It would be direct evidence of planets orbiting other stars at great distances. It would mean there could be another planet in our own solar system (unlikely, but I've written about that before). And it would mean that it's possible to use this method of near-infrared mapping to actually get pictures of more planets! Seeing one might be a fluke, seeing two means there are more to find.

The next clear night, do yourself a favor: go outside. Look up. See all those stars? Whether or not this particular planet pans out, we still know that a large fraction of those stars — 10%? 20? — may have planets. And some fraction of those may have planets like Earth orbiting them. We really weren't sure about this even 15 years ago, and now we're able to not only start plugging numbers into the equations, but we can actually take pictures of some of these objects.

My oh my. How I do love science.

source: Bad Astronomy

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03:52 - Shadow Cap
Category: Art and Photography

Shadow Cap

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The shadow of Saturn's rings sits upon the northern hemisphere of Mimas like a dark cap. In this Cassini view, which looks toward high northern latitudes on Mimas, the moon is just grazing the shadow of the rings.

Another view, PIA10467, was acquired a few minutes prior to this image, and shows a nearly identical Mimas (396 kilometers, 246 miles across) before the rings' shadow obscured the surface.

The two distinct shadow regions seen here are the penumbra and the much darker umbra. An observer within the penumbral region on Mimas would have their view the Sun partly blocked by the rings. For a viewer within the umbral region, the rings would completely cover the Sun. However, since the rings are not opaque, the Sun would still be dimly visible.

The image was brightened to reveal faint details within the eclipsed region, illuminated dimly by sunlight filtering through the rings.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 4, 2008. The view was acquired at a distance of approximately 143,000 kilometers (89,000 miles) from Mimas and from about 67 degrees above the moon's equator. The Sun-Mimas-spacecraft, or phase, angle in the image is 106 degrees. Image scale is 856 meters (2,808 feet) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Credit: NASA/JPL/Space Science Institute

Released: September 15, 2008

source: CICLOPS

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17:12 - The Joys of Rejection and Lake-effect clouds on Titan
Category: Goals, Plans, Hopes

The Joys of Rejection and Lake-effect clouds on Titan

Remember my new paper that describes my interesting discoveries about Titan (see Your Saturday Newspaper)? submitted it to Science magazine a few weeks ago in the hopes that it will be published and some day make it to your Saturday newspaper. But it won't. It has been rejected.

It was a kind rejection. They didn't say "we think you're paper is wrong." Just, "we don't find it of general enough interest to publish in our journal."

Rejection is always hard. My first response was generic sputtering "wha.. wha… what?" and then disbelief "this can't be!" and anger and dismissal "those idiots don't even know what they are missing." This sequence lasted about 7 seconds, and then I got over it. After about 1 minute I became excited.

Why be excited about rejection from Science? Along with the publicity benefits of publishing a paper in somewhere like Science comes the hard part. You agree not to publicize or discuss the paper before the publish it. This process can take 6 months or longer.

But having been rejected from Science, I quickly turned around and submitted the paper to a more specialized journal -- Geophysical Research Letters (aka GRL) -- which has no such restrictions, and then I went a step further and submitted it to an on-line electronic archive ( which means you can go read it right now! http://lanl.arxiv.org/abs/0809.1841).

Scientists these days are increasingly speeding up the slow process of formal publication with an informal process of web publication. Such web publication has good and bad aspects to it. Good: instant. Bad: unreviewed.

Anything that is published in a major journal has had one or two experts read it closely and suggest changes. My paper on Titan is currently undergoing this process at GRL, and, when the reviewers are done, I will modify and respond. But my paper is on the electronic archive for everyone to see before that even happens.

Posting a paper on-line before it has been reviewed can lead to great embarrassment. What if the paper has fundamental flaws and needs to be withdrawn or rejected? What if the referees point out places where major changes need to take part? All of this is certainly possible, and should make any on-line submitted wary. But, for me, the benefits outweigh the risks. I am sufficiently confident in the accuracy of what I did that I am not worried about any of these major problems. While there is no doubt that the reviewers will suggest some improvements, I don't believe the overall conclusions of the paper will change significantly. And I think the conclusions are sufficiently interesting that I relish the idea that people will begin to read the paper and think about the results now, rather than 6 months from now. So I submitted.

And now, even better, I can talk about the discovery of lake-effect clouds on Titan.

Earlier this summer, while looking through NASA's on-line archives of images of Saturn's satellite Titan taken from the Cassini mission, I began to notice a recurring pattern up near the north pole of the satellite. The north pole of Titan has been in the darkness throughout a long long winter (a full year on Titan takes 30 years; winter is almost a decade) and is just now emerging into some spring time daylight. As it began to emerge, I noticed what appeared to be tiny little clouds popping up and disappearing right over the pole.

Titan is in some ways bizarre and exotic yet in some ways very earth-like. Both earth and Titan have mostly-nitrogen atmospheres; on both the surface pressure is about the same (the big difference on Titan: it lacks that minor contaminant – oxygen – that makes the earth a more interesting place….).

Titan and earth are the only bodies in the solar system known to have large expanses of liquid at the surface. On Titan, though, the temperature is so low that water is frozen solid. The lakes of Titan are made, instead, of methane and ethane. If you could figure out a way to get a pipeline there, Titan's lakes could supply all of our needed natural gas for years to come.

On earth the liquid water is globally distributed. On Titan it appears that the liquid methane and ethane is confined to the poles.

Finally, Titan and earth both have clouds in its atmosphere, and these clouds are made from the dominant liquid on the surface. On earth: water. On Titan: methane.

Now, back to the little clouds I had seen popping up at the north pole during Titan's early spring.

These clouds surprised me; they appear to be cumulous clouds – like large thunder heads. On the earth we only get such clouds in hot, humid places. Arizona in August. Year-round in the tropics. Temperate latitudes during summer storms. How could such clouds possibly be up at the north pole just as winter is waning?

It occurred to me that we do get winter cumulus-type clouds on the earth in at least one case: lake-effect clouds and storms. Lake-effect storms on the earth are those winter storms that blow across the Great Lakes, pick up moisture, and then proceed to dump many many feet of snow on places like Buffalo, New York.

The effect occurs in many other places around the world. Or, I should say, they same effect occurs in many other places around the solar system. I believe this process is precisely what is causing the sporadic clouds at the north pole of Titan.

Like everything else, Titan and earth have similarities and differences in their lake-effect clouds, too. On the earth, the formation of these clouds is greatly aided by the fact that deep lakes stay relative warm over the winter. So as cold air passes over these lakes the air both picks up humidity and a little heat. This heat causes the air to rise (like a hot air balloon) which, in turn, causes those cumuli and the subsequent snow.

On Titan, a decade of polar winter means that none of the lakes retain any heat, so passing air only picks up humidity (methane humidity, in this case). Something else needs to help push the air higher to cause those cumuli. In the paper, we speculate that there might be mountains at the north pole that help, but really that is just a wild guess.

Cold lakes won't evaporate, so these clouds have only started to become active in the last few years as sunlight has started to every-so-slightly heat the lakes. Every time the lakes warm up just a bit, a huge dollop of evaporation occurs, which re-cools the lake, and we see a cumulus cloud pop up. The lake then has to wait for some more sunlight before it happens again.

If our general story is correct – and I think it is – then as spring and then summer approaches at the north pole, the sunlight will increase dramatically, and the lake-effect clouds will start to go crazy. And we'll be watching. The Cassini spacecraft is slated to continue flying past and taking pictures of Titan for several more years. And we might find more exciting things.

And what will we do when we find exciting things? Well, in the end I will probably never learn my lesson. We'll submit them to Science. Or we'll submit them to Nature. And then we will have to wait for months to talk about them. And maybe they will get a paragraph in your Saturday paper. But, if we – and you – are lucky, we will instead be rejected, we'll post to a freely available on-line archive, and everyone can hear early about the latest happenings on this bizarre satellite.

source: Mike Brown's Planets

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00:25 - Rosetta and Philae – the asterophilic couple
Category: Travel and Places

Rosetta and Philae – the asterophilic couple

Credits: ESA MPS for OSIRIS Team MPS/UPM/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

On September 6th, 2008, the ESA's space probe Rosetta performed the first highlight on its 11 year mission: a close flyby the asteroid 2867 Steins. There are two more important events to occur during the mission, which are another flyby the asteroid 21 Lutetia in 2010 and the actual rendezvous with the comet 67/P Churyumov-Gerasimenko in 2014.

The Rosetta mission is special in many ways. It is the first mission to deploy a lander to the surface of a comet. It will also be the first to orbit the nucleus of a comet and to fly alongside a comet as it heads towards the inner Solar System.

Credits: ESA

Rosetta's mission began on March 2nd, 2004, when the spacecraft lifted off from Kourou, French Guiana. In order to optimize the use of fuel, the probe has a very complicated trajectory to reach its final target, the comet 67/P Churyumov-Gerasimenko. The long trajectory includes three Earth-gravity assists (2004, 2007, and 2009) and one at Mars (2007). The probe uses the gravity wells of Earth and Mars to accelerate to the speed needed for the rendezvous with the comet. Most of the time, the probe is hibernating with the majority of its systems shut down in order to optimize the power consumption. At the time of the rendezvous, the remaining fuel will be used to slow down the probe to match the speed of the comet.

Credits: ESA/AOES Medialab

After reaching the comet, Rosetta will deploy a lander, called Philae, to the surface. While the probe will study the comet's nucleus from a close orbit, the lander will take measurements from the comet's surface. Because the gravity of the comet is very weak, the lander will use a harpoon to anchor itself to the surface.

Rosetta will stay with the comet more than one year, and during this time it will study one of the most primitive materials in the solar system. Scientists hope to discover the secrets of the physical and chemical processes that marked the beginning of the solar system some 5 billion years ago.

Credits: ESA/AOES Medialab

Traditionally, probes sent beyond the main asteroid belt employ radioisotope thermal generators (RTGs) as power generators. RTGs convert the heat from a radioactive source into electricity using an array of thermocouples. Instead, Rosetta is using solar cells for power generation. The probe deploys two impressive solar panels (a total area of 64 square meters). Even when close to the comet, the panels will be able to generate around 400 Watts of power. The panels can be rotated through +/- 180 degrees to track the Sun in every attitude assumed by the probe.

The probe is cube-shaped and measures 2.8×2.1×2.0 meters. At launch, it weighs 3,000 kg, including 1,670 kg of fuel, 165 kg of scientific payload for the orbiter, and 100 kg for the lander. The scientific instruments are accommodated on the lower side of the probe, which will be directed towards the comet during the last phase of the mission. Meanwhile, the probe will orbit the nucleus of the comet. A communication antenna 2.2 meters in diameter will be mounted on one side of the probe and on the opposite side the lander is attached. The other two lateral sides are used for anchoring the solar panels.

Credits: ESA/AOES Medialab

I was able to dig up more information about the probe and the lander in the mission launch kit on the EADS Astrium website.

The prime contractor for the spacecraft is Astrium Germany. The main sub-contractors are Astrium UK, Astrium France, and Alenia Spazio.

For propulsion and attitude control, the probe is using 24×10N bipropellant jets. The propulsion system is at the centre of the probe, where the tanks of propellant are located in the centre of a vertical tube.

I could not find an explanation as to why this design was chosen. Since the ability of the spacecraft to maneuver by using the onboard propulsion system is critical, I am assuming that the fuel tanks have to be protected from possible hits by micro meteorites.

Credits: ESA/AOES Medialab

The scientific instruments onboard Rosetta are: OSIRIS (Optical Spectroscopic and Infrared Remote Imaging System), ALICE (Ultraviolet Imaging Spectrometer), VIRTIS (Visible and Infrared Thermal Imaging System), MIRO (Microwave Instrument for Rosetta Orbiter), ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis), COSIMA (Cometary Secondary Ion Mass Analyser), MIDAS (Micro-Imaging Dust Analysis System), CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission), GIADA (Grain Impact Analyser and Dust Accumulator), RPC (Rosetta Plasma Consortium), and RSI (Radio Science Investigation).

The lander is provided by a European consortium lead by the DLR (German Aeronautic Research Institute). Members of this consortium include ESA and the Austrian, Finnish, French, Hungarian, Irish, Italian, and British institutes.

Credits: ESA/AOES Medialab

The lander has a polygonal carbon fibre sandwich structure which is covered in solar cells. The antenna transmits data from the lander via the probe orbiting the comet.

There is an impressive collection of scientific instruments mounted on the lander as well: COSAC (Cometary Sampling and Composition experiment), MODULUS PTOMELY (Gas analyser), MUPUS (Multi-Purpose Sensors for Surface and Subsurface Science), R