Stellar Nursary in the Rosette Nebula

Image credit: NOAO

A Chinese and US astronomer have discovered a young star at the heart of the Rosette Nebula that is ejecting a complex jet of material with knots and bow shocks. Normally these stars are hidden from the view of optical telescopes by the surrounding nebula, but severe ultraviolet radiation from nearby massive stars has cleared out the area. This gives astronomers have a rare opportunity to study how a young star like this forms. The Rosette Nebula is located 1,500 light-years away in the constellation of Monoceros.

A duo of Chinese and American astronomers have discovered a young star in the fierce environs of the Rosette Nebula that is ejecting a complex jet of material riddled with knots and bow shocks.

Stripped of its normally opaque surroundings by the intense ultraviolet radiation produced by nearby massive stars, this young stellar object is likely one of the last of its generation in this region of space. Its tenuous state of existence exposes the limitations that young stars?and perhaps even sub-stellar objects such as brown dwarfs and large planets?face in attempting to form in such a violent environment.

A close-up image from this study of the young star, and a striking, newly reprocessed wide-field image of the colorful Rosette Nebula, are available above.

?Most young stars are embedded in very dense molecular clouds, which makes our view of the early stages of star formation normally impossible with optical telescopes,? says Travis Rector of the University of Alaska Anchorage, co-author of a paper on the young stellar object (YSO) in the December 2003 issue of Astrophysical Journal Letters. ?This is one of only a few cases where a protostar is visible, making it a valuable discovery that will be studied in detail.?

Optical images of the jet taken at the WIYN 0.9-meter telescope at the National Science Foundation?s Kitt Peak National Observatory in Arizona show a highly-collimated jet, now known as Rosette HH1, stretching for more than 8,000 astronomical units (1 AU = 150 million kilometers). It contains a prominent knot and hints of others, which can be interpreted as ?bullets? of material being ejected from the rapidly rotating YSO at hypersonic velocities on the order of 2,500 kilometers per second. Bow shocks on the other side of the YSO suggest the existence of a degenerated counterjet extending in the opposite direction.

These interpretations of the jet were bolstered by optical spectroscopy of the jet system taken by co-author Jin Zeng Li of the Chinese Academy of Sciences in Beijing using the 2.16-meter telescope of the National Astronomical Observatories of China.

?If it is indeed a counterjet, it may be the only existing observational evidence of how bipolar jets evolve into monopoles, or at least highly asymmetric jets,? according to Jin Zeng Li. ?This suggests that this infant star has been starved of material as its accretion disk is evaporated, leaving a very low-mass star. In some cases, this process might result in an isolated brown dwarf or planetary mass object, offering a potential evolutionary solution for such lone objects that have been spotted in the Orion Nebula and other nearby hotspots in the Milky Way.?

Located an estimated 1,500 light-years from Earth in the constellation Monoceros, the Rosette Nebula is a spectacular region of ionized hydrogen excavated by the strong stellar winds from hot O- and B-type stars in the center of the young open cluster NGC 2244. It is a region of on-going star formation with an age of about three million years.

Kitt Peak National Observatory is part of the National Optical Astronomy Observatory, Tucson, Ariz., which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NOAO News Release

First Data from Mars Express

Image credit: ESA

The European Space Agency has gathered a mountain of new data from the Mars Express orbiter, which shows the Red Planet in unprecedented resolution – over the course of the last few weeks it’s gathered more than 100 GB of data. Its photographs show details as fine as sediments left on the bottom of river valleys and dust blowing over the rim of craters. The spacecraft is also detecting water being lost from the Martian atmosphere for the first time. Unfortunately, Mars Express still has yet to detect the British-built Beagle 2 lander, which went missing on December 25, 2003.

Mars Express, ESA?s first mission to Mars, will reach its final orbit on 28 January. It has already been producing stunning results since its first instrument was switched on, on 5 January. The significance of the first data was emphasised by the scientists at a European press conference today at ESA?s Space Operations Centre, Darmstadt, Germany.

“I did not expect to be able to gather together – just one month after the Mars Orbit Insertion of 25 December ? so many happy scientists eager to present their first results”, said Professor David Southwood, ESA Director of Science. One of the main targets of the Mars Express mission is to discover the presence of water in one of its chemical states. Through the initial mapping of the South polar cap on 18 January, OMEGA, the combined camera and infrared spectrometer, has already revealed the presence of water ice and carbon dioxide ice.

This information was confirmed by the PFS, a new high-resolution spectrometer of unprecedented accuracy. The first PFS data also show that the carbon oxide distribution is different in the northern and southern hemispheres of Mars.

The MaRS instrument, a sophisticated radio transmitter and receiver, emitted a first signal successfully on 21 January that was received on Earth through a 70- metre antenna in Australia after it was reflected and scattered from the surface of Mars. This new measurement technique allows the detection of the chemical composition of the Mars atmosphere, ionosphere and surface.

ASPERA, a plasma and energetic neutral atoms analyser, is aiming to answer the fundamental question of whether the solar wind erosion led to the present lack of water on Mars. The preliminary results show a difference in the characteristics between the impact of the solar wind area and the measurement made in the tail of Mars. Another exciting experiment was run by the SPICAM instrument (an ultraviolet and infrared spectrometer) during the first star occultation ever made at Mars. It has simultaneously measured the distribution of the ozone and water vapour, which has never been done before, revealing that there is more water vapour where there is less ozone.

ESA also presented astonishing pictures produced with the High Resolution Stereo Camera (HRSC). They represent the outcome of 1.87 million km2 of Martian surface coverage, and about 100 gigabytes of processed data. This camera was also able to make the longest swath (up to 4000 km) and largest area in combination with high resolution ever taken in the exploration of the Solar System.

This made it possible to create an impressive picture 24 metres long by 1.3 metres high, which was carried through the conference room at the end of the press event by a group of 10-year-old children.

Mrs Edelgard Bulmahn, German Minister for Research and Education, who is also chair of the ESA Council at Ministerial level, said at the press conference: “Europe can be proud of this mission: Mars Express is an enormous success for the European Space Programme.”

Original Source: ESA News Release

New Hubble Photos of Uranus and Neptune

Image credit: Hubble

New photographs from the Hubble Space Telescope show details of the atmospheres on Uranus and Neptune. The photos were taken using Hubble’s Imaging Spectrograph and Advanced Camera for Surveys in August 2003. Both planets have bands of clouds and haze lined up with the planets’ equators. Astronomers use different kinds of filters to reveal different kinds of gasses in the clouds, and even their altitudes above the planets.

Atmospheric features on Uranus and Neptune are revealed in images taken with the Space Telescope Imaging Spectrograph and the Advanced Camera for Surveys aboard NASA’s Hubble Space Telescope. The observations were taken in August 2003.

The top row reveals Uranus and Neptune in natural colors, showing the planets as they would appear if we could see them through a telescope. The images are made of exposures taken with filters sensitive to red, green, and blue light. In the bottom images, astronomers used different color filters to detect features we can’t see. The photographs demonstrate that, by using certain types of color filters, astronomers can extract more information about a celestial object than our eyes normally can see.

At first glance, the top row of images makes the planets appear like twins. But the bottom row reveals that Uranus and Neptune are two different worlds. Uranus’s rotational axis, for example, is tilted almost 90 degrees to Neptune’s axis. The south poles of Uranus and Neptune are at the left and bottom, respectively. Both are tilted slightly toward Earth. Uranus also displays more contrast between both hemispheres. This may be caused by its extreme seasons.

Both planets display a banding structure of clouds and hazes aligned parallel to the equator. Additionally, a few discrete cloud features appear bright orange or red. The color is due to methane absorption in the red part of the spectrum. Methane is third in abundance in the atmospheres of Uranus and Neptune after hydrogen and helium, which are both transparent. Colors in the bands correspond to variations in the altitude and thickness of hazes and clouds. The colors allow scientists to measure the altitudes of clouds from far away.

Original Source: Hubble News Release

Amateur Spots Close Passing Asteroid

Image credit: UA

A volunteer analyzing data gathered by the University of Arizona’s Spacewatch program has discovered an 18 x 36 metre asteroid that will miss the Earth by only 2 million kilometres today. Asteroid 2004 BV18 is no risk; even if it did hit the Earth, it wouldn’t do much more than cause a bright flash in the atmosphere. The asteroid was spotted by amateur astronomer Stu Megan, who was analyzing Spacewatch data through the Internet, and demonstrates how volunteers can help the search for near Earth asteroids.

A volunteer who analyzes online images for the University of Arizona Spacewatch program has discovered a 60-to-120-foot diameter asteroid that will miss Earth by about 1.2 million miles tomorrow, Jan. 22.

While the asteroid is no cause for alarm, its discovery marks a milestone in a new project that relies on volunteers to spot fast-moving objects, or FMOs, in Spacewatch images.

Even if asteroid 2004 BV18 hit Earth head-on, it would only create a bright flash of light in the upper atmosphere, and possibly streaks of light as asteroid fragments heat to incandescence while they rocket across the sky. “In other words, a bright meteoric display known as a bolide,” said Robert S. McMillan, who directs UA’s Spacewatch.

The asteroid appeared in images taken by Spacewatch astronomer Miwa Block with the 0.9-meter telescope at 1:49 UT on Jan. 19, which is 6:49 p.m. MST on Jan. 18. Volunteer Stu Megan reviewed the images on the Internet, and spotted the asteroid’s light trail. Megan is part of a Web-based program that Spacewatch made public last October through a grant from the Paul G. Allen Charitable Foundation.

“It’s hard to explain the excitement when you find a fast-moving asteroid,” Megan said in an E-mail message.

Megan is semi-retired from a 35-year career in information technology and an amateur astronomer who is interested in finding potentially hazardous asteroids. A resident of Tucson, he has reviewed close to 6,500 Spacewatch images during the past three months.

“When I saw (this light trail), it just sat there screaming at me. It was very, very bright and a perfect length. I knew it could be nothing else.”

Three observatories made follow-up observations of the asteroid, so scientists at the Minor Planet Center could compute its orbit. The Minor Planet Center gave Asteroid 2004 BV18 its provisional designation yesterday. (A provisional designation is one that’s adopted until the asteroid’s orbit is known well enough that astronomers won’t lose it.) The center also published the discovery and follow-up studies in the Minor Planet Electronic Circular yesterday.

The asteroid is classified as an “Apollo” asteroid because it is on average slightly farther from the sun than the Earth is, but its modest orbital eccentricity causes it to occasionally cross Earth’s orbit.

At the time Megan discovered the asteroid, it was six times farther from Earth than the Earth is from the moon. Seen from Earth, it appeared to move across the sky at about 6.5 degrees per day, or about the diameter of 13 full moons. At closest approach tomorrow, it will be five times the distance between Earth and the moon.

Spacewatch operates 1.8-meter and 0.9-meter CCD-equipped telescopes on Kitt Peak, about 45 miles southwest of Tucson, Ariz. The project studies solar system dynamics through the movements of asteroids and comets. Spacewatch also finds potential targets for interplanetary spacecraft missions and hunts for objects that might pose a threat to Earth.

The 0.9-meter telescope typically takes two-minute-long exposures, and objects closest to Earth move so quickly through the telescope’s field of view that they trace a line on the sky image. Objects orbiting farther from Earth appear to move more slowly, just as an airplane flying at 40,000 feet appears to move slower than it does at takeoff.

Computer software has a hard time detecting FMO light trails because they vary greatly in length and direction.

Human observers are still much better than computers at finding FMOs in Spacewatch images. But the work is too time intensive for on-duty Spacewatch observers. So the astronomers have turned to 30 volunteers for help. FMO project volunteers are based in the United States, Germany, and Finland.

They would gladly accept more.

The only requirements are interest, sharp eyes, and access to a computer when astronomers are operating Spacewatch telescopes on Kitt Peak. More details on how to volunteer for the FMO Project are on the Web at FMO Project.

“Our reviewers are students, people with full-time jobs, retired ? they run the gamut,” McMillan said. “While our most dedicated volunteers tend to be members of the amateur astronomy community or at least have a strong interest and knowledge of astronomy, we have members who have just begun to climb the learning curve.

“We hope that our Website helps fuel curiosity and participation in science in general, as well as provide a productive outlet for those eager to apply their computer skills,” McMillan said.

McMillan’s Spacewatch team protects the privacy of its volunteers, releasing volunteers’ names only to the Minor Planet Center when discoveries are to be published.

Astronomers want to study small asteroids to know how many there are, their spin rates and surface properties, McMillan said.

Spin rate tells observers if the asteroid is a single solid piece or a loose aggregate of rocks.

The distribution of asteroid sizes tells scientists about the effects of asteroid collisions during the lifetime of the solar system.

The smallest asteroids are free of regoliths, the blanket of loose dust or dirt that obscures the bare rock surfaces of larger asteroids. And the smallest asteroids are useful for studying non-gravitational forces that work on very long time scales, such as the Yarkovsky Effect, a phenomenon where heat propels objects through space.

The Spacewatch Project was begun in 1980 at the UA Lunar and Planetary Laboratory. More information about Spacewatch can be found on the Web at Spacewatch.

Original Source: UA News Release

New Earth Measurement Data Released

Image credit: NASA

NASA has released detailed topographical data of Europe and Asia that was gathered by the space shuttle as part of the 10-day Shuttle Radar Topography Mission (SRTM) in February 2000 that mapped 80% of the Earth’s surface. This data represents 40-percent of the data collected during the mission. North and South American data has already been made available, and the remainder should be completed by 2004. This precise 3-D mapping information is being used in many applications, including studying natural disasters, planning development, and aircraft navigation.

Marco Polo. Alexander the Great. They were some of history’s most prolific explorers, each trekking across sweeping stretches of Europe and Asia in their lifetimes. But these greats of world history had nothing on you, thanks to a new topographic data set from NASA and the National Geospatial-Intelligence Agency (NGA). You now can explore the vast reaches of most of Europe, Asia and numerous islands in the Indian and Pacific Oceans, from the comfort of home, without breaking a sweat.

Gathered in just 10 days by NASA’s Shuttle Radar Topography Mission (SRTM) in February 2000, the new digital elevation data set showcases some of Earth’s most diverse, mysterious and extreme topography. Much of it previously had been very poorly mapped due to persistent cloud cover or inaccessible terrain. The new data being released comprise more than one-third of the entire SRTM data set.

The new images are available on the JPL Planetary Photojournal at:

“People around the world will benefit from the release of the SRTM Europe and Asia topographic data sets because they greatly extend our knowledge of this immense region that also is home to most of Earth’s citizens,” said Dr. John LaBrecque, manager, Solid Earth and Natural Hazards Program, NASA Headquarters, Washington.

“The shape of Earth’s surface affects nearly every natural process and human endeavor. Precise, uniform, 3-D elevation data are needed for a wide range of applications from studying earthquakes, volcanism, floods and other natural hazards, to planning development, managing precious water resources, and insuring the safety of aircraft navigation,” LaBrecque noted.

“Releasing the Eurasia SRTM data provides geospatial data users with a remarkably consistent Earth-elevation surface. This enhances our global knowledge, provides a baseline for any future comparisons, and delivers accuracy and integrity unparalleled in any other global-elevation model of the Earth,” said NGA’s Technical Executive Roberta Lenczowski. “This SRTM data represents 40 percent of the data collected during the mission that covered roughly 80 percent of the landmass of the Earth. The cooperative effort between NASA and NGA, fusing science objectives with national security requirements, benefits all,” Lenczowski added.

The area covered in the current data-release stretches eastward from the British Isles and the Iberian Peninsula in the west, across the Alps and Carpathian Mountains, as well as the Northern European Plain, to the Ural and Caucasus Mountains bordering Asia. The Asian coverage includes a great variety of landforms, including the Tibetan Plateau, Tarim Basin, Mongolian Plateau and the mountains surrounding Lake Baikal, the world’s deepest lake. Mt. Everest in the Himalayas, at 8,848 meters (29,029 feet) is the world’s highest mountain. From India’s Deccan Plateau, to Southeast Asia, coastal China, and Korea, various landforms place constraints on land-use planning during periods of population growth. Volcanoes in the East Indies, the Philippines, Japan and the Kamchatka Peninsula form the western part of the “Ring of Fire” around the Pacific Ocean.

Previous releases from the mission covered North and South America. Forthcoming releases in 2004 will include Africa-Arabia and Australia, as well as an “islands” release for those islands not included in the continental data-releases. Together, these data-releases constitute the world’s first high-resolution, near-global elevation model. The resolution of these data for Europe and Asia is three arc seconds (1/1,200 of a degree of latitude and longitude), which is about 90 meters (295 feet).

The SRTM mission is a cooperative project of NASA, NGA and the German and Italian space agencies. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., processed the data into research-quality digital elevation data. The National Geospatial-Intelligence Agency is providing additional processing to develop mapping products. The U.S. Geological Survey Earth Resources Observation Systems Data Center in Sioux Falls, S.D., provides final archiving and distribution of the SRTM data products.

Information about SRTM is available at:

More information about NASA is at:

Original Source: NASA News Release

Distance to Pleiades Calculated

Image credit: NOAO

Astronomers from NASA’s Jet Propulsion Laboratory have measured the distance to the Pleiades star cluster to greatest precision ever. After a decade’s worth of interferometric measurements, the team found that the star cluster is between 434 and 446 light years from Earth. This is important because the European Hipparcos satellite previously measured a distance to the cluster that would have contradicted theoretical models of the life cycles of stars. This new measurement shows that Hipparcos was incorrect, and the established theory still holds.

The cluster of stars known as the Pleiades is one of the most recognizable objects in the night sky, and for millennia has been celebrated in literature and legend. Now, a group of astronomers has obtained a highly accurate distance to one of the stars of the Pleiades known since antiquity as Atlas. The new results will be useful in the longstanding effort to improve the cosmic distance scale, and to conduct research on the stellar life-cycle.

In the January 22 issue of the journal Nature, astronomers from the California Institute of Technology and NASA?s Jet Propulsion Laboratory, both in Pasadena, Calif., report the best-ever distance to the double-star Atlas. The star, along with “wife” Pleione and their daughters, the “seven sisters,” are the principal stars of the Pleiades that are visible to the unaided eye, although there are actually thousands of stars in the cluster. Atlas, according to the team’s decade of careful interferometric measurements, is somewhere between 434 and 446 light-years from Earth.

The range of distance to the Pleiades cluster may seem somewhat imprecise, but in fact is accurate by astronomical standards. The traditional method of measuring distance is by noting the precise position of a star and then measuring its slight change in position when Earth itself has moved to the other side of the sun. This approach can also be used to find distance on Earth: If you carefully record the position of a tree an unknown distance away, move a specific distance to your side, and measure how far the tree has apparently “moved,” then it’s possible to calculate the actual distance to the tree by using trigonometry.

However, this procedure gives only a rough distance estimate to even the nearest stars, due to the gigantic distances involved and the subtle changes in stellar position that must be measured.

The team’s new measurement settles a controversy that arose when the European satellite Hipparcos provided a much shorter distance measurement to the Pleiades than expected and contradicted theoretical models of the life cycles of stars.

This contradiction was due to the physical laws of luminosity and its relationship to distance. A 100-watt light bulb one mile away looks exactly as bright as a 25- watt light bulb half a mile away. So to figure out the wattage of a distant light bulb, we have to know how far away it is. Similarly, to figure out the “wattage” (luminosity) of observed stars, we have to measure how far away they are. Theoretical models of the internal structure and nuclear reactions of stars of known mass also predict their luminosities. So the theory and measurements can be compared.

However, the Hipparcos data provided a distance lower than that assumed from the theoretical models, thereby suggesting either that the Hipparcos distance measurements themselves were off, or else that there was something wrong with the models of the life cycles of stars. The new results show that the Hipparcos data was in error, and that the models of stellar evolution are indeed sound.

The new results come from careful observation of the orbit of Atlas and its companion — a binary relationship that wasn’t conclusively demonstrated until 1974 and certainly was unknown to ancient watchers of the sky. Using data from the Mount Wilson stellar interferometer, next to the historic Mount Wilson Observatory, and the Palomar Testbed Interferometer at Caltech’s Palomar Observatory near San Diego, the team determined a precise orbit of the binary.

Interferometry is an advanced technique that allows, among other things, for the “splitting” of two bodies so far away that they normally appear as a single blur, even in the biggest telescopes. Knowing the orbital period and combining it with orbital mechanics allowed the team to infer the distance between the two bodies, and with this information, to calculate the distance of the binary to Earth.

“For many months I had a hard time believing our distance estimate was 10 percent larger than that published by the Hipparcos team,” said the lead author, Xiao Pei Pan of JPL. “Finally, after intensive rechecking, I became confident of our result.”

Coauthor Shrinivas Kulkarni, a Caltech astronomy and planetary science professor, said, “Our distance estimate shows that all is well in the heavens. Stellar models used by astronomers are vindicated by our value.”

“Interferometry is a young technique in astronomy and our result paves the way for wonderful returns from the Keck interferometer and the anticipated Space Interferometry Mission that is expected to be launched in 2009,” said coauthor Michael Shao of JPL, prinicipal investigator for that planned mission, and for the Keck Interferometer, which links the two 10-meter telescopes at the Keck Observatory in Hawaii. The Palomar Testbed Interferometer was designed and built by a team of researchers from JPL led by Mark Colavita and Shao. It served as an engineering testbed for the Keck Interferometer.

Original Source: NASA/JPL News Release

Weather on Earth is a Problem for Spirit

Image credit: NASA/JPL

A thunderstorm in Australia has hampered communications between NASA and the Spirit rover on Mars. The rover was supposed to use its Rock Abrasion Tool (RAT) to grind into the rock 5 mm, but the weather interfered with the commands sent from Earth. When it doesn’t receive orders from Earth, Spirit goes into a stasis mode where it runs checks on its systems, and takes photographs of its surroundings. Engineers are hoping to try again tonight.

Ground controllers were able to send commands to the Mars Exploration Rover Spirit early Wednesday and received a simple signal acknowledging that the rover heard them, but they did not receive expected scientific and engineering data during scheduled communication passes during the rest of that martian day.

Project managers have not yet determined the cause, but similar events occurred several times during the Mars Pathfinder mission. The team is examining a number of different scenarios, some of which would be resolved when the rover wakes up after powering down at the end of the martian day (around midday Pacific time Wednesday).

The next opportunity to hear from the vehicle is when the rover may attempt to communicate with the Mars Global Surveyor orbiter at about 8:30 p.m. Pacific time tonight. A second communication opportunity may occur about two hours later during a relay pass via the Mars Odyssey orbiter. If necessary, the flight team will take additional recovery steps early Thursday morning (the morning of sol 19 on Mars) when the rover wakes up and can communicate directly with Earth.

Full details on the rover’s status will be described in the next daily news conference Thursday at 9 a.m. Pacific time at the Jet Propulsion Laboratory, which will be broadcast live on NASA Television.

Original Source: NASA/JPL News Release

Next Steps for Beagle 2

Image credit: Beagle2

Controllers initiated a state of radio silence with the Beagle 2 lander after it failed to report in, or communicate through Mars Express. In theory this radio silence should force Beagle 2 to enter into “Communication Mode 2”, where it attempts to call out constantly throughout the Martian day. The best opportunities to make contact with the lander will happen on the nights of January 24/25 when Mars Express passes over a significant portion of the landing area.

On 12 January a period of radio silence was initiated when no attempts were made to contact Beagle 2. Maintaining radio silence for a period of ten days is intended to force Beagle 2 into a communication mode that should ensure that the transmitter is switched on for the majority of the daytime on Mars and thus will improve the chance of the Mars Express orbiter making contact.

During this ten-day period Mars Express has listened for Beagle 2 but only for very short periods when Beagle 2 may not have been switched on.

The ten-day radio silence period ends today [22 January], just before a fly-over by Mars Express. However, it is not intended to hail the Lander immediately. This cautious approach is based on the fact that the end of the ten-day period of radio silence cannot be predicted with total confidence. This is because the absolute accuracy of the timer on Beagle 2 could have been affected by the temperature on Mars, making the clock run slightly faster or slower than predicted.

It has therefore been decided to choose a pair of opportunities when Mars Express flies over the Beagle 2 landing site, namely the nights of 24 and 25 January. These two flights cover the widest possible area where Beagle 2 should be, giving the best chance of calling the Lander and getting a response from the continuous transmission.

The results from these latest attempts to communicate with Beagle 2 will be announced by Prof. Colin Pillinger, Beagle 2 Lead Scientist and Dr. Mark Sims, Beagle 2 Mission Manager, on 26 January, at a media briefing to be held at The Science Media Centre, The Royal Institution of Great Britain, 21 Albemarle Street, London W1S 4BS, at 1400 GMT.

Original Source: PPARC News Release

Selecting Stars Very Similar to Our Own

Image credit: John Rowe

The search for Earthlike planets begins with the search for Sunlike stars. At the top of the list is a reasonably nearby star called 37 Gem; located in the Gemini constellation. Astronomer Maggie Turnbull was asked to make a short list of thirty candidate stars that closely matched our own Sun out of a total list 2,350 stars which are within one hundred light years from us. This short list, including 37 Gem will be used by the Terrestrial Planet Finder mission, which will search for habitable planets by looking for the visible light of oxygen or water in an Earthlike planet – a sure sign of life.

The thirty-seventh most westerly star in the constellation, Gemini, is a yellow-orange star like our own sun. The star is called 37 Geminorum, but for astrophysicist Margaret Turnbull, the star is special because it offers a case study for considering what might qualify as a good candidate for harboring habitable planets.

In building her list of stars that might support planets with liquid water and oxygen, she has to exclude suns that are extreme: either too young or too old, that rotate too fast, or that are variable enough in brightness to cause climatic chaos on any nearby world.

At a distance of 56.3 light-years away, the star 37 Gem has yet to show tell-tale signs of having such planets, or any planets–but future NASA and European telescopes are looking to target stars just like 37 Gem since they might share some of the same properties that made our own solar system habitable. More than 100 extrasolar planets have been found so far using ground-based telescopes, and estimates for the total such planets in our galaxy may total in the billions of candidate worlds.

Working from the University of Arizona in Tucson, Maggie Turnbull was asked to make a short list of thirty star candidates that most closely resembled other suns capable of supporting the conditions for life to flourish. Starting her search among stars less than one hundred light-years away yielded about 2,350 stars to consider further.

Turnbull recently presented her results to a group of scientists from NASA’s space-telescope project, the Terrestrial Planet Finder (TPF), which will search for habitable planets by using visible light with the “signature” of water and/or oxygen from an Earth-type planet. After TPF’s scheduled launch around 2013, will follow the European Darwin project involving six space telescopes.

The stellar list was pared down from an even larger list (17,129 stars within 450 light-years, or 140 parsecs), which Turnbull and adviser Jill Tarter of the SETI Institute first published in Astrophysical Journal. The list became known as the Catalog of Nearby Habitable Stellar Systems (or HabCat ). Their article published in August, entitled “Target Selection for SETI: I. A Catalog of Nearby Habitable Stellar Systems,” expanded previous candidate lists by nearly ten-fold, or an order-of-magnitude.

To support complex life, a candidate star must be the right color, brightness, and age. If it is a middle-aged star like our own, it will have burned through enough fusionable light elements to produce heavier metals like iron, but not so old that it is collapsing or so young that life is only a distant future prospect. Based on what fragments we know about how complex life appeared on Earth, Turnbull’s search aims to find the ‘Goldilocks’ of stars that seems ‘just right’.

So why 37 Gem?
37 Geminorum lies in the northwest part of constellation Gemini , named after the Twins. For amateur astronomers with a good backyard telescope, 37 Gem is visible. In Greek mythology, the Gemini twins sailed with Jason in the quest for the Golden Fleece; during a storm, the twins helped save their ship ARGO from sinking, and so the constellation became much valued by sailors.

Most stars like Gem 37 are grouped into a small number of spectral classes, based roughly on the color of light they emit. Called the Henry Draper Catalog, the star compendium lists spectral classes in seven broad categories, from the hottest to the coolest stars. These types are designated, in order of decreasing temperature, by the letters O, B, A, F, G, K, and M. The nomenclature is rooted in long-obsolete ideas about stellar evolution, but the terminology remains. Our sun, classified on a finer scale as a typical ‘G2V’ dwarf, is approximately 4.5 billion years old. The candidate star, 37 Gem, is similarly middle-aged, but somewhat older by a billion years, at 5.5 billion years.

The spectra of G-type stars like our own (and 37 Gem) are dominated by certain chemical elements, as signaled by their characteristic spectral lines (or emissions). The elements of most current interest are metals, particularly for those star-signatures rich in iron, calcium, sodium, magnesium, and titanium. In astronomical terms, compared to our sun’s classification as a typical G2V dwarf, 37 Gem has a slightly hotter surface temperature. Thus Turnbull’s prime pick–37 Gem– is catalogued as a G0V dwarf–meaning it is also a yellow-orange main sequence dwarf star. Because G stars are characterized by the presence of these metallic lines and a weak hydrogen spectra, they share a common age, mass, and luminosity.

Otherwise, 37 Gem is close to our own solar twin, or a Gemini-like counterpart to the Sun: 1.1 times our sun’s mass, 1.03 times its diameter, and 1.25 times its luminosity.

Luminosities are “perhaps the most important information”, Turnbull told Astrobiology Magazine, “we use in determining the habitability of nearby stars” for complex life, because luminosity indicates which phase of life the star is in, and that in turn dictates how long the star will remain stable.

Astrobiology Magazine had the opportunity to talk with Maggie Turnbull at the Steward Observatory in Tucson about how to select stellar candidates for habitability.

Astrobiology Magazine (AM): Your recent survey began looking at around 100-light years distant from our Sun, and all stars inwards from that radius, correct? That was the visual sphere for starting the search?

Margaret Turnbull (MT): There are about 2,350 Hipparcos stars within 30 parsecs (90 light
years), the maximum distance for the Terrestrial Planet Finder (TPF) mission. There are about 5,000 total stars within that distance, but we are only looking at Hipparcos stars so my starting list is 2,350 stars long.

AM: Have you ever gotten hold of a backyard telescope to see 37 Gem?

MT: It should certainly be visible with a backyard telescope, but no, I haven’t looked at it with my own eyes! Because of the photometry (measuring its brightness) and spectroscopy (measuring its composition) I have looked at, I feel like I “know” it without ever having seen it.

However, there is more observing to be done for 37 Gem. For example, we do need to carry out high resolution infrared imaging of this star before we can say it should be a target–if we discover that there is a lot of debris floating around, we’ll have to take it off the list.

AM: Was the star, 37 Gem, much different from number two on the list of the thirty best candidates?

MT: Actually, the “best” stars are all very similar to one another, and in reality it doesn’t make much sense to try to rank them. 37 Gem happens to be one of the very nearest stars that also satisfies the engineering criteria, so at this time it looks like a very good candidate for the TPF search.

AM: Just out of curiousity, what star was officially number two on the list?

MT: When you are only going to look at thirty stars, they all better be “number one.” That is, every star we observe has to be of primary interest to the mission, because we have no time to waste. We are still in the process of precisely defining the primary mission goal.

If the goal is to look at range of spectral types, then the top stars may include very nearby K or M stars, but if the goal is to look at 30 of the most Sun-like stars, then stars like 18 Sco (a solar twin at 14 parsecs in the Constellation Scorpius), beta CVn (the “hound”), or 51 Peg (“Pegasus”, the flying horse) may end up being our best bets.

AM: Are there one or two pieces of missing data that would help the classification hone in better on star candidates?

MT: At this time, high-resolution infrared imaging is the missing piece of data that we definitely need. We need to know if these stars have dusty debris disks that would make it hard to detect planets orbiting there.

The Sun has a substantial amount of zodiacal dust because Jupiter is constantly stirring up the asteroid belt and as the asteroids collide they add dust to the Solar System.

A similar level of dust around other stars might not ruin our chances of seeing planets, but we’d certainly like to keep that to a minimum.

AM: What are your future plans for the stellar list in support of the Terrestrial Planet Finder and Darwin missions?

MT: I haven’t yet presented my ‘final’ list to the TPF science working group on Nov 18th and 19th at the US Naval Observatory, during a meeting with others who are creating their own lists.

I have already presented my methodology to the group, but now we will be meeting with engineers who will explain to us the constraints of the instrument and we will have to refine further the list to accommodate their criteria.

Their criteria will include things like: can’t have a companion star within several arcseconds even if the companion is not a concern for planet stability, because the extra light will contaminate the field of view; can’t look at stars fainter than about 6th magnitude; can only look at stars at least ~60 degrees away from the Sun during the whole year, etc.

AM: You published your first catalog of habitable stars in August of this year, and there is a part two to that classification. What are the main plans for Part II of the HabCat?

MT: Jill Tarter and I have recently submitted a second paper on the SETI target list which will appear in the Astrophysical Journal Supplements in December. This paper gives a list of old, high metallicity open clusters, the nearest 100 stars regardless of stellar type, and about 250,000 main sequence stars from the Tycho Catalogue, all of which will be observed by the Allen Telescope Array (ATA) whenever a HabCat star isn’t available for us to observe.

The primary ATA beam will be pointed by radio astronomers, and they will be making very high resolution maps of their own targets, while at the same time we will be observing HabCat stars (or stars from our lists in Paper 2) for SETI.

AM: Finally, are the missions, Kepler and TPF, planning the kinds of enhancements that would yield a detection of more Earth-sized planets, not just gas giants, for a given star in their surveys?

MT: Yes. Kepler will give us an indication of how common terrestrial planets are by watching thousands of sun-like stars for “transits”–events where the planet actually passes in front of the star it is orbiting and temporarily blocks a little of the star’s light.

Terrestrial Planet Finder will follow up on this by actually imaging planets orbiting the nearest stars, and telling us whether these planets have atmopheres by taking spectra.

We can look for water, oxygen, and carbon dioxide, and if we’re lucky we may even see some direct indications of life in the form of a vegetation signature or strong atmospheric disequilibrium, such as the simultaneous presence of oxygen and methane (due to the simultaneous presence of plants and methanogen bacteria on Earth).

What’s Next
Any mission to detect and spectroscopically characterize terrestrial planets around other stars must be designed so that it can detect diverse types of terrestrial planets with a useful outcome. Such missions are now under study–the Terrestrial Planet Finder (TPF), by NASA, and Darwin by ESA, the European Space Agency. The principal goal of TPF/Darwin is to provide data to the biologists and atmospheric chemists.

The TPF/Darwin concept hinges on the assumption that one can screen extrasolar planets for habitability spectroscopically. For such an assumption to be valid, we must answer the following questions. What makes a planet habitable and how can they be studied remotely? What are the diverse effects that biota might exert on the spectra of planetary atmospheres? What false positives might we expect? What are the evolutionary histories of atmospheres likely to be? And, especially, what are robust indicators of life?

TPF/Darwin must survey nearby stars for planetary systems that include terrestrial sized planets in their habitable zones (“Earth-like” planets). Through spectroscopy, TPF/Darwin must determine whether these planets have atmospheres and establish whether they are habitable.

The Kepler mission is also scheduled for launch into solar orbit in October 2006. Kepler is intended as a mission to determine the frequency of inner planets near the habitable zone of a wide range of stars. Kepler will simultaneously observe 100,000 stars in our galactic “neighborhood,” looking for Earth-sized or larger planets within the “habitable zone” around each star – the not-too-hot, not-too-cold zone where liquid water might exist on a planet.

To highlight the difficulty of detecting an Earth-sized planet orbiting a distant star, Kepler’s principal investigator, William Borucki of NASA Ames points out it would take 10,000 Earths to cover the Sun’s disk. One NASA estimate says Kepler should discover 50 terrestrial planets if most of those found are about Earth’s size, 185 planets if most are 30 percent larger than Earth and 640 if most are 2.2 times Earth’s size. In addition, Kepler is expected to find almost 900 giant planets close to their stars and about 30 giants orbiting at Jupiter-like distances from their parent stars.

Because most of the gas giant planets found so far orbit much closer to their stars than Jupiter does to the Sun, Borucki believes that during the four- to six-year mission, Kepler will find a large proportion of planets quite close to stars. If that proves true, he says, “We expect to find thousands of planets.”

Using present methods, astronomers today would find it very difficult to detect an Earth-sized planet around the star 37 Gem. Past analyses have however ruled out some choices. For instance, a giant planet like our own Jupiter or Saturn does not orbit around 37 Gem. These studies have suggested that giant planets of one-tenth to 10 times the mass of Jupiter do not exist close to 37 Gem (within 0.1 to four astronomical units, or one earth-sun distance, AUs, see also Cummings et al, 1999 ). Because of the challenges of finding dim planets near to much brighter stars, almost all of the extrasolar planets found so far are like our own Jupiter–massive, probably gaseous, and unlikely to harbor conditions for life owing to their close proximity to a parent star.

But conditions around 37 Gem might support smaller, inner planets like Venus or Earth. No one knows. Only future surveys will have the instrumentation capable of finding such Earth-like planets.

Models of stars like 37 Gem, do however, support the possible existence of at least one stable orbit for an Earth-like planet (with liquid water) centered around one earth-sun distance (1.12 AU). Such a presumed planet would orbit between the distances of Earth and Mars in our Solar System. This undiscovered planet, if it can be detected in future studies, would have a year that lasts more than 450 days, or an orbital period of around 1.3 Earth-years.

Since oxygen-generating life on Earth took about two billion years to take hold, stars much younger than this would likely not have had sufficient time for life to evolve towards any complex forms. Given the billions of years required for evolution of life on earth, scientists could question whether life would stand a chance in a shorter-lived solar system. Hotter, more massive stars have always been considered less likely to harbor life but not because they would be too hot. Planets could still enjoy temperate climates, just further out than Earth is from the Sun, and at orbits farther away from the its own parent star. The first problem of habitability is one of time, not temperature. Hotter stars tend to burn out faster — perhaps too fast for life to develop there.

Original Source: Astrobiology Magazine

Spirit Reaches Out to Adirondack

Image credit: NASA/JPL

Spirit is reaching out to test the nearby rock, “Adirondack”, which controllers targeted to get a better understanding of its composition and origin; it will be performing a series of tests today and tonight. The rover already used its instruments to examine a patch of soil near the lander and found some surprising results: the soil in Gusev Crater seems volcanic in origin, not sedimentary. Its instruments have also found the presence of a mineral called olivine, which doesn’t resist weathering very well and is normally evidence of volcanic deposits.

The first use of the tools on the arm of NASA’s Mars Exploration Rover Spirit reveals puzzles about the soil it examined and raises anticipation about what the tool will find during its studies of a martian rock.

Today and overnight tonight, Spirit is using its microscope and two up-close spectrometers on a football-sized rock called Adirondack, said Jennifer Trosper, mission manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

“We’re really happy with the way the spacecraft continues to work for us,” Trosper said. The large amount of data — nearly 100 megabits — transmitted from Spirit in a single relay session through NASA’s Mars Odyssey spacecraft today “is like getting an upgrade to our Internet connection.”

Scientists today reported initial impressions from using Spirit’s alpha particle X-ray spectrometer, Moessbauer spectrometer and microscopic imager on a patch of soil that was directly in front of the rover after Spirit drove off its lander Jan. 15.

“We’re starting to put together a picture of what the soil at this particular place in Gusev Crater is like. There are some puzzles and there are surprises,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the suite of instruments on Spirit and on Spirit’s twin, Opportunity.

One unexpected finding was the Moessbauer spectrometer’s detection of a mineral called olivine, which does not survive weathering well. This spectrometer identifies different types of iron-containing minerals; scientists believe many of the minerals on Mars contain iron. “This soil contains a mixture of minerals, and each mineral has its own distinctive Moessbauer pattern, like a fingerprint,” said Dr. Goestar Klingelhoefer of Johannes Gutenberg University, Mainz, Germany, lead scientist for this instrument.

The lack of weathering suggested by the presence of olivine might be evidence that the soil particles are finely ground volcanic material, Squyres said. Another possible explanation is that the soil layer where the measurements were taken is extremely thin, and the olivine is actually in a rock under the soil.

Scientists were also surprised by how little the soil was disturbed when Spirit’s robotic arm pressed the Moessbauer spectrometer’s contact plate directly onto the patch being examined. Microscopic images from before and after that pressing showed almost no change. “I thought it would scrunch down the soil particles,” Squyres said. “Nothing collapsed. What is holding these grains together?”

Information from another instrument on the arm, an alpha particle X- ray spectrometer, may point to an answer. This instrument “measures X-ray radiation emitted by Mars samples, and from this data we can derive the elemental composition of martian soils and rocks,” said Dr. Johannes Brueckner, rover science team member from the Max Planck Institute for Chemistry, Mainz, Germany. The instrument found the most prevalent elements in the soil patch were silicon and iron. It also found significant levels of chlorine and sulfur, characteristic of soils at previous martian landing sites but unlike soil composition on Earth.

Squyres said, “There may be sulfates and chlorides binding the little particles together.” Those types of salts could be left behind by evaporating water, or could come from volcanic eruptions, he said. The soil may not have even originated anywhere near Spirit’s landing site, because Mars has dust storms that redistribute fine particles around the planet. The next target for use of the rover’s full set of instruments is a rock, which is more likely to have originated nearby.

Spirit landed in the Connecticut-sized Gusev Crater on Jan. 3 (EST and PST; Jan. 4 Universal Time). In coming weeks and months, according to plans, it will examine rocks and soil for clues about whether the past environment there was ever watery and possibly suitable to sustaining life. Spirit’s twin Mars Exploration Rover, Opportunity, will reach Mars on Jan. 25 (EST and Universal Time; 9:05 p.m., Jan. 24, PST) to begin a similar examination of a site on the opposite side of the planet.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at and from Cornell University, Ithaca, N.Y., at .

Original Source: NASA/JPL News Release