Posted on by Fraser Cain

Largest Core in an Extrasolar Planet

Artist illustration of the planet orbiting the sun-like star HD 149026. Image credit: U.C. Santa Cruz. Click to enlarge.
NASA researchers recently discovered the largest solid core ever found in an extrasolar planet, and their discovery confirms a planet formation theory.

“For theorists, the discovery of a planet with such a large core is as important as the discovery of the first extrasolar planet around the star 51 Pegasi in 1995,” said Shigeru Ida, theorist from the Tokyo Institute of Technology, Japan.

When a consortium of American, Japanese and Chilean astronomers first looked at this planet, they expected one similar to Jupiter. “None of our models predicted that nature could make a planet like the one we are studying,” said Bun’ei Sato, consortium member and postdoctoral fellow at Okayama Astrophysical Observatory, Japan.

Scientists have rarely had opportunities like this to collect such solid evidence about planet formation. More than 150 extrasolar planets have been discovered by observing changes in the speed of a star, as it moves toward and away from Earth. The changes in speed are caused by the gravitational pull of planets.

This planet also passes in front of its star and dims the starlight. “When that happens, we are able to calculate the physical size of the planet, whether it has a solid core, and even what its atmosphere is like,” said Debra Fischer. She is consortium team leader and professor of astronomy at San Francisco State University, Calif.

The planet, orbiting the sun-like star HD 149026, is roughly equal in mass to Saturn, but it is significantly smaller in diameter. It takes just 2.87 days to circle its star, and the upper atmosphere temperature is approximately 2,000 degrees Fahrenheit. Modeling of the planet’s structure shows it has a solid core approximately 70 times Earth’s mass.

This is the first observational evidence that proves the “core accretion” theory about how planets are formed. Scientists have two competing but viable theories about planet formation.

In the “gravitational instability” theory, planets form during a rapid collapse of a dense cloud. With the “core accretion” theory, planets start as small rock-ice cores that grow as they gravitationally acquire additional mass. Scientists believe the large, rocky core of this planet could not have formed by cloud collapse. They think it must have grown a core first, and then acquired gas.

“This is a confirmation of the core accretion theory for planet formation and evidence that planets of this kind should exist in abundance,” said Greg Henry, an astronomer at Tennessee State University, Nashville. He detected the dimming of the star by the planet with his robotic telescopes at Fairborn Observatory in Mount Hopkins, Arizona.

Original Source: NASA News Release

Posted on by Fraser Cain

Hubble’s View of Deep Impact

Hubble’s view of the Deep Impact collision. Image credit: Hubble. Click to enlarge.
The NASA/ESA Hubble Space Telescope captured the dramatic effects of the collision early on 4 July between the Deep Impact impactor spacecraft and Comet 9P/Tempel 1.

This sequence of images shows the comet before and after the impact. The image at left shows the comet just minutes before the impact. The encounter occurred at 07:52 CEST (05:52 UT/GMT).

In the middle image, captured 15 minutes after the collision, Tempel 1 appears four times brighter than in the pre-impact photograph.

Astronomers noticed that the inner cloud of dust and gas surrounding the comet’s nucleus increased by about 200 kilometres in size.

The impact caused a brilliant flash of light and a constant increase in the brightness of the inner cloud of dust and gas.

Hubble continued to monitor the comet, snapping another image (at right) 62 minutes after the encounter. In this photograph, the gas and dust ejected during the impact are expanding outward in the shape of a fan.

The fan-shaped debris is travelling at about 1800 kilometres an hour, or twice as fast as the speed of a commercial jet. The debris extends about 1800 kilometres from the nucleus.

The potato-shaped comet is 14 kilometres wide and 4 kilometres long. Tempel 1’s nucleus is too small even for the Hubble telescope to resolve.

The visible-light images were taken by the high-resolution camera on Advanced Camera for Surveys instrument. The Hubble Space Telescope is a project of international co-operation between ESA and NASA.

Original Source: ESA/Hubble News Release

Posted on by Fraser Cain

What’s Up This Week – July 4 – July 10, 2005

The “Cat’s Eye” Nebula. Image credit: Chris Deforeit at Astrim. Click to enlarge.
Monday, July 4 – 1054 A.D. This is the suspected date when Chinese astronomers noted the supernova from which we know the remnants of today as M1, the “Crab Nebula”. While this incredible event marks a red letter day in astronomy history, another is in the making.

If everything goes successfully, Deep Impact will have already been released and the information pouring in. For most of us, tonight will be our first chance to view, but for the lucky astronomers in the extreme western Americas – you’ve beat us to it! Just 3.5 degrees east/northeast of Spica, the comet is speculated to rise to 6th magnitude as the debris cloud spreads. No one knows exactly how long this will last, but viewers around the globe will get their opportunity to witness this event with a backyard telescope over the next 24 hours. Be there! I wish you all the very best of skies for this event.

So, if we can’t see a supernova remnant like the M1, or watch explosion happen on a comet, then what else can we do tonight? I’ve got a great idea – let’s check out the “Cat’s Eye” – it’s the best of both worlds! The proper designation is NGC 6543 and it’s located about midway between Delta and Zeta Draconis. As one of the most complex of all the planetary nebulae, it rose to popularity with the awesome Hubble photo. Very similar to the “Helix” nebula, our blue-green friend is the ejecta of a dying (possible double) star. This colorful planetary sends its light to us from roughly 3200 light years away and was the very first to be studied spectroscopically.

At magnitude 8.8, the “Cat’s Eye” can be spotted in large binoculars but will appear almost stellar. Smaller telescopes at high power will make it out as a slight disc, while larger scopes reveal the central star and far more color. For those with a nebular filter and a large scope, the NGC 6543 is a real pleasure to study as the helical area takes on form. Enjoy!

Tuesday, July 5 – Today as the date changes, the Earth reaches aphelion its farthest point from the Sun for the year while – oddly enough – Comet 9/P Tempel 1 reaches perihelion. So where’s the comet?

For northern hemisphere binocular users, look for the point of light visible to the southwest at twilight. That’s Jupiter. As the sky darkens completely, bright Spica will appear to Jupiter’s southeast. By aiming your binoculars there and placing Spica to the right of the field of view, you should be able to spot a faint fuzzy – the comet! For telescope users, Tempel 1 will appear almost directly between both star 68 and Gamma Virginis. Although we cannot perfectly predict what will happen after Deep Impact, studies suggest the comet will brighten to around 6th magnitude. Even if it doesn’t seem particularly impressive to smaller equipment, remember… You are viewing history! This will be the first time mankind has ever been able to make an effect on an astronomical object that can be viewed by the amateur.

If skies are cloudy tonight, keep trying. The effect of Deep Impact may last for days – or even weeks. The comet will continue to move south slowly over the next two weeks when it will be just west of Gamma Virginis.

Wednesday, July 6 – With some help from Edmond Halley, today in 1687 Sir Isaac Newton published his Principia with his three laws of motion. Since New Moon occurred in the early morning hours, this means dark skies tonight and an opportunity to study.

Normally, we’d go galaxy hunting on a dark night such as this, but how about if we explore the wonderful world of low power? Start by locating the magnificent M13 and move about 3 degrees northwest. What you will find is a splendid loose open cluster of stars known as Dolidze/Dzimselejsvili (DoDz) 5 – and it looks much like a miniature of the constellation of Hercules. Just slightly more than 4 degrees to its east and just about a degree south of Eta Hercules is DoDz 6, which contains a perfect diamond pattern and an asterism of brighter stars which resembles the constellation of Saggitta.

Now we’re going to move across the constellation of Hercules towards Lyra. East of the “keystone” you will see a tight configuration of three stars – Omicron, Nu and Xi. About the same distance that separates these stars to the northeast you will find DoDz 9. Using minimal magnification, you’ll see a pretty open cluster of around two dozen mixed magnitude stars that are quite attractive. Now look again at the “keystone” and identify Lambda and Delta to its south. About midway between them and slightly to the southeast you will discover the stellar field of DoDz 8. The last is easy – all you need to do is know beautiful red/green double, Ras Algethi (Alpha). Move about 1 degree to the northwest to discover the star-studded open cluster – DoDz 7. These great open clusters are very much off the beaten path and will add a new dimension to your large binocular, or low power telescoping experiences.

Thursday, July 7 – Are you ready for a visual challenge? Then see if you can spot the ultra-slim crescent of the Moon tonight. Less than a fist’s width above the horizon, look about 45 minutes after sunset as Selene begins its showing with the planets.

Tonight let’s try two more open star cluster studies that can be done easily with large binoculars or a low power scope. The first is a rich beauty that lays in the constellation of Vulpecula, but is easier found by moving around 3 degrees southeast of Beta Cygni. Known as Stock 1, this stellar swarm contains around 50 or so members of varying magnitudes that you will return to often. The next is an asterism known as the “Coat Hanger”, but it is also known as Brocchi’s Cluster, or Collinder 399. Let the colorful double star – Albeiro (which can be split in binos) – be your guide as you move about 4 degrees to its south/southwest. You will know this cluster when you see it, because it really does look like a coat hanger! Enjoy its red stars.

Friday, July 8 – What a way to start the weekend! As the skies darken to twilight tonight, be sure to check out the western horizon as the tender Moon has risen above our planetary pair of Venus and Mercury. Loaded with “earthshine”, this should be a picture perfect evening.

If skies are clear, let’s try some open star clusters in Cygnus. Starting with Gamma, identify loose open involving Gamma named Dolidze (Do) 43. Move two degrees southwest and pick up Do 42. Do not confuse it with nearby M29 – for the two look very similar. For fans of the “Double Cluster” in Perseus, you’ll like the next as we move another half degree to the southwest along the body of Cygnus to discover Do 40 and Do 41. This pretty pair of open clusters can be placed in the same lower power field. By moving another half degree due west, you’ll find highly populated Do 39 and it is a double treat as well – the brighter clump of stars in the same low power field is IC 4996.

Saturday, July 9 – Tonight the Moon will be less than half a fist’s width away from the “heart of Leo”, Regulus. While you may need binoculars to spot the star, be sure to note both it and Venus’ position and watch over the next two weeks as they draw closer.

Tonight after the Moon sets, take out your binoculars again to view two bright open clusters. The first, Ruprecht 173 is about a degree northwest of Epsilon Cygnii. You’ll appreciate this heavily populated star cluster! The next is as easy as identifying the constellation of Lyra. Just southeast of bright Vega is a wonderful double for binoculars, Delta 1 and 2 – the easternmost of the top two stars in the lyre. This bright pair is part of an open cluster known as Stephenson 1.

Sunday, July 10 – Tonight let’s enjoy a quiet evening of lunar contemplation. A wonderful crater to watch over the coming days lay on the western edge of Mare Crisium – Proculus. Tonight you will see it as a bright ring, but it will soon develop a ray system as the terminator moves west. Another beautiful pair of craters are near the terminator in the northern quandrant of the lunar orb – Atlas and Hercules. They are a splendid sight in binoculars and scope users can easily spot interior craterlets in these old giants.

Even if you only follow Deep Impact virtually, please watch this spectacular event. We’ll be on hand for history! May all your journeys be at Light Speed… ~Tammy Plotner

Posted on by Fraser Cain

Deep Impact Releases Impactor

Deep Impact took this image of its own impactor drifting away from the spacecraft. Image credit: NASA/JPL. Click to enlarge.
One hundred and seventy-one days into its 172-day journey to comet Tempel 1, NASA’s Deep Impact spacecraft successfully released its impactor at 11:07 p.m. Saturday, Pacific Daylight Time (2:07 a.m. Sunday, Eastern Daylight Time).

At release, the impactor was about 880,000 kilometers (547,000 miles) away from its quarry. The separation of flyby spacecraft and the washing-machine-sized, copper-fortified impactor is one in a series of important mission milestones that will cap off with a planned encounter with the comet at 10:52 p.m. Sunday, PDT (1:52 a.m. on July 4, EDT).

Six hours prior to impactor release, the Deep Impact spacecraft successfully performed its fourth trajectory correction maneuver. The 30-second burn changed the spacecraft’s velocity by about one kilometer per hour (less than one mile per hour). The goal of the burn is to place the impactor as close as possible to the direct path of onrushing comet Tempel 1.

Soon after the trajectory maneuver was completed, the impactor engineers began the final steps that would lead to it being ready for free flight. The plan culminated with activation of the impactor’s batteries at 10:12 p.m., PDT (1:12 a.m. Sunday, EDT). Deep Impact’s impactor has no solar cells; the vehicle’s batteries are expected to provide all the power required for its short day-long life.

In order to release the impactor, separation pyros fired allowing a spring to uncoil and separate the two spacecraft at a speed of about 35 centimeters per second (0.78 mile per hour).

With Tempel 1 closing the distance between it and impactor at about 10 kilometers (6 miles) per second, there is little time for mission controllers to admire their work. Twelve minutes after impactor release the flyby began a 14-minute long divert burn that slowed its velocity relative to the impactor by 102 meters per second (227 miles per hour), moving it out of the path of the onrushing comet nucleus and setting the stage for a ringside seat of celestial fireworks to come less than 24 hours later.

Deep Impact mission controllers have confirmed the impactor’s S-band antenna is talking to the flyby spacecraft. All impactor data including the expected remarkable images of its final dive into the comet’s nucleus will be transmitted to the flyby craft — which will then downlink them to Deep Space Network antennas that are listening 134 million kilometers (83 million miles) away.

While all is going as expected on the Deep Impact spacecraft the comet itself is putting on something of a show. The 14-kilometer-long (8.7-mile-long) comet Tempel 1 displayed another cometary outburst on July 2 at 1:34 a.m. PDT (4:34 a.m.EDT) when a massive, short-lived blast of ice or other particles escaped from inside the comet’s nucleus and temporarily expanded the size and reflectivity of the cloud of dust and gas (coma) that surrounds it. The July 2 outburst is the fourth observed in the past three weeks.

Three of the outbursts appear to have originated from the same area on the surface of the nucleus but they do not occur every time that that area faces the Sun.

“The comet is definitely full of surprises so far and probably has a few more in store for us,” said Deep Impact Project Manager Rick Grammier of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “None of this overly concerns us nor has it forced us to modify our nominal mission plan.”

Information and images from a camera aboard Deep Impact’s impactor and flyby spacecraft can be watched in near-real time at http://www.nasa.gov/deepimpact.

For additional information about Deep Impact on the Internet, visit NASA Deep Impact.

Original Source: NASA News Release

Posted on by Fraser Cain

Happy Canada Day!

Hi folks, it’s Canada Day today here, so I’m taking the day off . Universe Today will be back on Monday with plenty of fresh space news.

Fraser Cain
Publisher
Universe Today

Posted on by Fraser Cain

Podcast: Interview with Story Musgrave

How many times have I been to space? Well, I lost count at, oh, none. So I, and nearly every other human being on Earth can’t compare with Story Musgrave, a legendary NASA astronaut who flew on the space shuttle six times, including leading the team that fixed the Hubble Space Telescope’s vision in 1993. He’s the subject of a recent biography called Story: the Way of Water, and has a new CD called Cosmic Fireflies, which sets his space inspired poetry to music. Story speaks to me from his home in Florida.
Continue reading “Podcast: Interview with Story Musgrave”

Posted on by Fraser Cain

Positron Drive: Fill ‘er Up For Pluto

Computer illustration of a potential antimatter drive. Image credit: Positronics Research LLC. Click to enlarge.
We all played the game as children – “leapfrog” involved one child squatting on all fours while a second placed their hands on the first’s shoulders. Braced against the pull of gravity, the standing child bends at the legs deeply then thrusts up and over the top of the first. The result? The second child now squats and the another froglike leap follows in turn. Not the most efficient way to get to the swing set – but a lot of fun in the right company!

Leapfrogging however is not the same as ‘bootstrapping’. While bootstrapping, a single player bends and grabs the leather loops on the outside of both boots. The player then makes a tremendous exertion upward with the arms. Leapfrogging works – bootstrapping doesn’t, it just can’t be done without hopping – an entirely different thing altogether.

The NASA Institute for Advanced Concepts (NIAC) believes in leapfrogging – no not on the playground but in aerospace. From the institutes own website: “NIAC encourages proposers to think decades into the future in pursuit of concepts that will “leapfrog” the evolution of current aerospace systems.” NIAC is looking for a few good ideas and is willing to support them with six-month-long seed grants to test feasibility before serious research and development funds – available from NASA and elsewhere – are allocated. Hopefully such seeds are allowed to germinate and future investment grows them to maturity.

NIAC wants to separate out leapfrogging from bootstrapping, however. One works and the other makes no sense whatsoever. According to NIAC, the positron drive could lead to a giant leap forward in the way we travel throughout the solar system and beyond. There’s probably no bootstrapping about it.

Consider the positron – mirror twin of the electron – like human twins, a very rare thing. Unlike human twins, a positron is unlikely to survive the birth process. Why? Because positrons and their siblings – electrons – find each other irresistible and quickly annihilate in a burst of soft gamma rays. But that burst, under controlled circumstances, can be converted into any form of ‘work’ you might want to do.

Need light? Mix a positron and an electron then irradiate a gas to incandescence. Need electricity? Mix another pair and irradiate a metal strip. Need thrust? Shoot those gamma rays into a propellant, heat it to outlandishly high temperatures and push the propellant out the back of the rocket. Or, shoot those gamma rays into tungsten plates in a stream of air, heat that air and jettison it out the back of an aircraft.

Imagine having a supply of positrons – what could you do with them? According to Gerald A. Smith, Principle Investigator for Positronics Research, LLC of Sante Fe, New Mexico you could go just about anywhere, “the energy density of antimatter is ten orders of magnitude greater than chemical and three orders of magnitude greater than nuclear fission or fusion energy.”

And what does this mean in terms of propulsion? “Less weight, far, far, far less weight.”

Using chemically based propulsion systems, 55 percent of the weight associated with the Huygens-Cassini probe sent to explore Saturn was found in the probe’s fuel and oxidizer tanks. Meanwhile to hurl the probes 5650 kg of weight beyond the Earth required a launch vehicle weighing some 180 times that of fully-fueled Cassini-Huygens itself (1,032,350 kgs).

Using Dr. Smith’s numbers alone – and only considering the maneuvering thrust required for Cassini-Huygens using positron-electron annihilation, the 3100 kgs of chemical propellant burdening the original 1997 probe could be reduced to a mere 310 micrograms of electrons and positrons – less matter than that found in a single atomized drop of morning mist. And with this reduction in mass the total launch weight from Canaveral to Saturn could easily be reduced by a factor of two.

But positron-electron annihilation is like having plenty of air but absolutely no gasoline ? your car won?t get far on oxygen alone. Electrons are everywhere, while positrons are not naturally available on Earth. In fact where they do occur – near black hole event horizons or for short periods of time after high energy particles enter the Earth’s atmosphere – they soon find one of those ubiquitous electrons and go photonic. For this reason you have to make your own.

Enter the particle accelerator
Companies such as Positronics Research, headed up by Dr. Smith, are working on technologies inherent in the use of particle accelerators – like the Stanford Linear Accelerator (SLAC) located in Menlo Park, California. Particle accelerators create positrons using electron-positron pair-production techniques. This is done by smashing a relativistically accelerated electron beam into a dense tungsten target. The electron beam is then converted into high energy photons which move through the tungsten and turn into matched sets of electrons and positrons. The problem before Dr. Smith and others creating positrons is easier than trapping, storing, transporting, and using them effectively.

Meanwhile during pair-production, all you’ve really done is packed a whole lot of earth-bound energy into extremely small amounts of highly volatile – but extremely light-weight – fuel. That process itself is extremely inefficient and introduces major technical challenges related to accumulating enough anti-particles to power a spacecraft capable of journeying into the Great Beyond at velocities making large space probe – and human spacetravel – possible. How is all this likely to play out?

According to Dr. Smith, “for many years physicists have squeezed positrons out of the tungsten targets by colliding the positrons with matter, slowing them down by a thousand or so to use in high resolution microscopes. This process is horribly inefficient; only one millionth of the positrons survive. For space travel we need to increase the slowing down efficiency by at least a factor of one thousand. After four years of hard work with electromagnetic traps in our labs, we are preparing to capture and cool five trillion positrons per second in the next few years. Our long-range goals are five quad-trillion positrons per second. At this rate we could fuel up for our first positron-fueled flight into space in a matter of hours.”

While it is true that a positron-annihilation engine also requires propellent (typically in the form of compressed hydrogen gas), the amount of propellant itself is reduced to almost 10 percent of that required by a conventional rocket – since no oxidizer is needed to react with the fuel. Meanwhile, future craft may actually be able to scoop propellant up from the solar wind and interstellar medium. This should also lead to a significant reduction in the launch weight of such spacecraft.

Written by Jeff Barbour

Posted on by Fraser Cain

New Method Pinpoints the Age of the Milky Way

One of the meteorites analyzed to help pinpoint the age of Milky Way. Image credit: Nicolas Dauphas, University of Chicago. Click to enlarge.
The University of Chicago?s Nicolas Dauphas has developed a new way to calculate the age of the Milky Way that is free of the unvalidated assumptions that have plagued previous methods. Dauphas? method, which he reports in the June 29 issue of the journal Nature, can now be used to tackle other mysteries of the cosmos that have remained unsolved for decades.

?Age determinations are crucial to a fundamental understanding of the universe,? said Thomas Rauscher, an assistant professor of physics and astronomy at the University of Basel in Switzerland. ?The wide range of implications is what makes Nicolas? work so exciting and important.?

Dauphas, an Assistant Professor in Geophysical Sciences, operates the Origins Laboratory at the University of Chicago. His wide-ranging interests include the origins of Earth?s atmosphere, the oldest rocks that may contain evidence for life on Earth and what meteorites reveal about the formation of the solar system.

In his latest work, Dauphas has honed the accuracy of the cosmic clock by comparing the decay of two long-lived radioactive elements, uranium-238 and thorium-232. According to Dauphas? new method, the age of the Milky Way is approximately 14.5 billion years, plus or minus more than 2 billion years.

That age generally agrees with the estimate of 12.2 billion years?nearly as old as the universe itself? as determined by previously existing methods. Dauphas? finding verifies what was already suspected, despite the drawbacks of existing methods: ?After the big bang, it did not take much time for large structures to form, including our Milky Way galaxy,? he said.

The age of 12 billion years for the galaxy relied on the characteristics of two different sets of stars, globular clusters and white dwarfs. But this estimate depends on assumptions about stellar evolution and nuclear physics that scientists have yet to substantiate to their complete satisfaction.

Globular clusters are clusters of stars that exist on the outskirts of a galaxy. The processes of stellar evolution suggested that most of the stars in globular clusters are nearly as old as the galaxy itself. When the big bang occurred 13.7 billion years ago, the only elements in the universe were hydrogen, helium and a small quantity of lithium. The Milky Way?s globular clusters have to be nearly that old because they contain mostly hydrogen and helium. Younger stars contain heavier elements that were recycled from the remains of older stars, which initially forged these heavier elements in their cores via nuclear fusion.

White dwarf stars, meanwhile, are stars that have used up their fuel and have advanced to the last stage of their lives. ?The white dwarf has no source of energy, so it just cools down. If you look at its temperature and you know how fast it cools, then you can approximate the age of the galaxy, because some of these white dwarfs are about as old as the galaxy,? Dauphas said.

A more direct way to calculate the age of stars and the Milky Way depends on the accuracy of the uranium/thorium clock. Scientists can telescopically detect the optical ?fingerprints? of the chemical elements. Using this capability, they have measured the uranium/thorium ratio in a single old star that resides in the halo of the Milky Way.

Original Source: University of Chicago News Release

Posted on by Fraser Cain

Rosetta Tunes in Tempel 1

Rosetta’s photograph of Comet Tempel 1, it’s down on the lower left. Image credit: ESA. Click to enlarge.
ESA?s Rosetta comet-chaser spacecraft has acquired its first view of the Deep Impact target, Comet 9P/Tempel 1.

This first Rosetta image of the Deep Impact campaign was taken by its Navigation Camera (NAVCAM) between 08:45 and 09:15 CEST on 28 June 2005.

The image shows that the spacecraft now points towards Comet 9P/Tempel 1 in the correct orientation. The NAVCAM is pointing purposely slightly off-target to give the best view to the science instrumentation.

The NAVCAM system on board Rosetta was activated for the first time on 25 July 2004. This system, comprising two separate independent camera units (for back-up), will help to navigate the spacecraft near the nucleus of Comet 67P/Churyumov-Gerasimenko in ten years time.

In the meantime though, the cameras can also be used to track other objects, such as Comet Tempel 1, and the two asteroids that Rosetta will be visiting during its long cruise, Steins and Lutetia.

The cameras perform both as star sensors and imaging cameras (but not with the same high resolution as some of its other instruments), and switch functions by means of a refocusing system in front of the first lens.

The magnitude of Comet Tempel 1 is at the detection limit of the camera: it is not as easily visible in the raw image and the image here is a composite of 20 exposures of 30 seconds each.

The comet is the fuzzy object with the tail in the lower left of the image. The faintest stars visible in this image are about 13th magnitude, the bright star in the upper left is about 8th magnitude. The image covers about 0.5 degrees square, and celestial north is to the right.

Original Source: ESA News Release