Extrasolar Planets Archives

March 13, 2008December 26, 2015 by Ian O'Neill

Could AA Tauri Hold the Biochemical Key to Extra-Terrestrial Life?

NASA’s Spitzer Space Telescope has measured huge quantities of water and organic compounds surrounding the star AA Tauri, 450 light years from Earth. AA Tauri is a young star, only a million years old, not too dissimilar to our Sun when it was a baby. What makes AA Tauri even more special is that it appears to have the “spectral fingerprint” for a system that could allow life to form. Finding a star system similar to our own, with organic compounds was always bound to cause excitement, but finding a star so close to us provides a fantastic opportunity to study AA Tauri. This will, in turn, help us understand the evolution of our own solar system and how life is able to form…

AA Tauri is slowly evolving. Gas and dust surrounds the star and recent observations suggest there are abundant organic chemicals (the ones responsible for binding together and creating amino acids). Although NASA’s announcement isn’t claiming that ET is out there (you can sit back into your seats), it is significant that a star should have all the building blocks for life as we know it laid out for the spectrometer on board Spitzer to observe.

The basic organic chemicals in question are possibly located within the “Goldilocks Zone” for planetary/life development from AA Tauri. Although AA Tauri is young, the surrounding flat disk of planetary-forming materials should eventually coalesce to form rocky bodies such as planets, asteroids and possibly gas giants (along the lines of “failed star” Jupiter). The abundance of organic chemicals and water will add to the intrigue surrounding the star.

These observations were collected by NASA’s Spitzer Space Telescope which is able to probe deep into the chemical structure of stars hundreds of parsecs from Earth. John Carr (Naval Research Laboratory, Washington) and Joan Najita (National Optical Astronomy Observatory, Tucson, Ariz.) are developing a new technique, applying Spitzer’s infrared spectrograph. The spectrograph is able to read the chemical composition of the dust contained within a protoplanetary disk. The team has been able to push Spitzer to a new level of precision by analysing the chemical composition of dust particles rather than the gas surrounding the star.

“Most of the material within the disks is gas, but until now it has been difficult to study the gas composition in the regions where planets should form. Much more attention has been given to the solid dust particles, which are easier to observe.” – John Carr of the Naval Research Laboratory, Washington.

So far abundances of hydrogen cyanide, acetylene, carbon dioxide and water vapour have been discovered, allowing scientists to see whether these organic chemicals are enriched or lost during the violent period of planetary formation. Observations such as these highly accurate measurements allow us a chance to glimpse back in time to see what our protoplanetary solar system may have looked like, clearly a very exciting time for the quest to find the origins of life in our galaxy.

Source: NASA/JPL

March 10, 2008December 26, 2015 by Fraser Cain

Are There Planets Around Alpha Centauri?

We’re holding out hope for the next generation of planet-finding observatories to locate Earth-sized planets orbiting other stars. But hold on, maybe we don’t need a super space observatory like ESA’s Darwin just yet. In fact, if our nearest neighbour Alpha Centauri has Earth-sized planets, we should be able to detect them with established techniques… right now, with the observatories we have today.

University of California researcher Javiera Guedes has developed a computer simulation that shows that Alpha Centauri B – the largest star in the nearby triple-star system – should have terrestrial planets orbiting within its habitable zone, where liquid water can exist.

They ran several simulations of the system’s first 200 million years. In each instance, despite different parameters, multiple terrestrial planets formed around the star. In every case, at least one planet turned up similar in size to the Earth, and in many cases this planet fell within the star’s habitable zone.

Guedes and co-author Gregory Laughlin think there are several reasons why Alpha Centauri B makes an excellent candidate for finding terrestrial planets. Perhaps the best reason is that Alpha Centauri is just so close, located a mere 4.3 light years away. But it’s also positioned well in the sky, giving it a long period of observability from the Southern Hemisphere.

Most of the 228 extrasolar planets discovered to date have been with the Doppler technique. This is where a planet pulls its parent star back and forth with its gravity. The star’s relative velocity in space changes the wavelength of light coming from it which astronomers can detect. Until now, only the largest planets, orbiting at extremely close distances from their parent stars have been discovered.

But with a nearby star like Alpha Centauri B, much smaller planets could be detected.

The researchers are proposing that astronomers dedicate a single 1.5-metre telescope to intensively monitor Alpha Centauri over a period of 5 years. In that time, any change in the star’s light should be detectable by this telescope.

“If they exist, we can observe them,” said Guedes.

Original Source: UCSC News Release

February 20, 2008December 26, 2015 by Fraser Cain

Planet Hunter Prepped for Tests

If you think the discoveries made by planet hunters is exciting already, just you wait. There are some missions in the works that are going multiply the number of planets discovered, and zoom in on the holy grail of finding habitable planets around other stars. The next planet hunter being readied for launch is NASA’s Kepler Mission. This week engineers conducted a series of tests on its image detectors – will it really be able to see planets?

Scheduled for launch in 2009, Kepler will detect planets using the transit method. This is where a planet passes in front of its parent star, briefly dimming the amount of light we see here on Earth. This has been done to detect Jupiter-scale planets, but nothing Earth-sized… yet.

Kepler will have sensitive enough instruments to be able to detect those slight variations in brightness, and determine just how many stars have planets in their habitable zones.

At the Ames Research Center, researchers have developed a Kepler Technology Demonstration test bed. This generates a field of stars that matches the part of the sky where mission scientists are planning to search for transits. The testing engineers can then modify the brightness of the artificial stars to mimic how transiting planets would look as they passed in front of stars.

“This is a major milestone for the Kepler mission,” said David Koch, deputy principal investigator for the Kepler Mission. “We will use hardware identical to what we will be flying on Kepler in the test bed at Ames. We will have the ability to create transits of a star so that we can see the change in the starâ€™s brightness. By simulating transits, we will be able to demonstrate that the flight hardware will work,” Koch explained.

In the final mission, Kepler will be equipped with 42 CCD cameras attached to the spacecraft’s telescope. They make up a 30-cm square (1-foot) array; the largest that will have been flown in space to date. The spacecraft will be able to scan a region of the sky 30,000 times larger than Hubble is able to search.

This month’s test at AMES will have only a single CCD detector, measuring 2.5 cm by 5 cm (1-inch by 2-inches).

I’ll give you an update once the tests are run. Those habitable planets can’t hide forever.

Original Source: NASA News Release

February 18, 2008December 26, 2015 by Nancy Atkinson

Rocky Planets May Form Around Most Sun-like Stars

Astronomers have found numerous Jupiter-like planets orbiting other stars. But because of the limits of our current technology, they haven’t yet found any other terrestrial Earth-like planets out in the universe. But new findings from the Spitzer Space Telescope suggest that terrestrial planets might form around many, if not most, of the nearby sun-like stars in our galaxy. So perhaps, other worlds with the potential for life might be more common than we thought.

A group of astronomers led by Michael Meyer of the University of Tucson, Arizona used Spitzer to survey six sets of stars with masses comparable to our sun, and grouped them by age.

“We wanted to study the evolution of the gas and dust around stars similar to the sun and compare the results with what we think the solar system looked like at earlier stages during its evolution,” Meyer said. Our sun is about 4.6 billion years old.

They found that at least 20 percent, and possibly as many as 60 percent, of stars similar to the sun are candidates for forming rocky planets.

The Spitzer telescope does not detect planets directly. Instead, using its infrared capability, it detects dust — the rubble left over from collisions as planets form — at a range of infrared wavelengths. Because dust closer to the star is hotter than dust farther from the star, the “warm” dust indicates material orbiting the star at distances comparable to the distance between Earth and Jupiter.

Meyer said that about 10 to 20 percent of the stars in the four youngest age groups shows ‘warm’ dust, but not in stars older than 300 million years. That is comparable to the theoretical models of our own solar system, which suggests that Earth formed over a span of 10 to 50 million years from collisions between smaller bodies.

But the numbers are vague on how many stars are actually forming planets because there’s more than one way to interpret the Spitzer data. “An optimistic scenario would suggest that the biggest, most massive disks would undergo the runaway collision process first and assemble their planets quickly. That’s what we could be seeing in the youngest stars. Their disks live hard and die young, shining brightly early on, then fading,” Meyer said.

“However, smaller, less massive disks will light up later. Planet formation in this case is delayed because there are fewer particles to collide with each other.”

If this is correct and the most massive disks form their planets first and then the smaller disks take 10 to 100 times longer, then up to 62 percent of the surveyed stars have formed, or may be forming, planets. “The correct answer probably lies somewhere between the pessimistic case of less than 20 percent and optimistic case of more than 60 percent,” Meyer said.

In October 2007, another group of astronomers used similar Spitzer data to observe the formation of a star system 424 light-years away, with another possible Earth-like planet being created.

More definitive data on formation of rocky planets will come with the launch the Kepler mission in 2009, which will search to find if terrestrial planets like Earth could be common around stars like the sun.

Original News Source: JPL Press Release

February 14, 2008December 26, 2015 by Fraser Cain

Another Solar System Found with Saturn and Jupiter-Sized Planets

As the search for extrasolar planets continues, researchers are finding systems more and more like our own Solar System. And today researchers announced another significant find: a system with two planets smaller than Jupiter and Saturn. It’s almost starting to sound like home.

The report, due to be published in the February 15th edition of the journal Science discusses a series of observations made back on March 28, 2006. An experiment, known as the Optical Gravitational Microlensing Equipment (OGLE), detected the telltale signal of a microlensing event on a star 5,000 light-years away.

In case you weren’t up in the latest techniques for planetary discovery, a lensing event happens when two stars line up perfectly in the sky from our perspective on Earth. The closer star acts as a natural lens, magnifying the light from the more distant star.

The curve of light coming from the event is very specific, and astronomers know when they’re seeing a microlensing event, compared to something else like a nova or a variable star.

But there are special situations, where the light from the star brightens normally, but then has an additional distortion. The gravity from planets orbiting the closer star can actually create this additional distortion. And from this, astronomers can calculate their size (amazing!). Only 4 planets had been discovered this way so far.

Okay, enough back story.

The OGLE group announced their potential lensing event, and astronomers around the world sprung into action, gathering data for the entire time that the stars were lined up.

Researchers first calculated that there was a Saturn-sized planet orbiting the star, and then another group found that there had to be a Jupiter-sized planet as well.

“Even though we observed the micolensing effect of the Saturn for less than 0.3 percent of its orbit, the observations simply could not be explained without accounting for the orbit,ï¿½? said David Bennett, a research associate professor of astrophysics from the University of Notre Dame.

Unfortunately, viewing this planetary system was a one-time event. We’ll probably never see this star line up again, so there’s no way to perform any followup observations.

Original Source: University of Notre Dame News Release

February 11, 2008December 26, 2015 by Fraser Cain

Lightweight Disk Could Harbour Planets

Astronomers are looking for planets around other stars, but they’re also looking for the conditions where planets might be forming right now. Inside the disks of material that surround newly forming planets, they could be planets clearing paths through all the gas and dust. A team of Japanese astronomers have found the most lightweight stellar disk ever seen – a place where Earth-sized planets could be forming.

Using the powerful Subaru telescope, located atop Hawaii’s Mauna Kea, a team of astronomers from several Japanese universities have resolved a lightweight disk of material around a nearby, and relatively tiny star called FN Tau. It’s probably only 100,000 years old, and contains a mere 1/10th the mass of our own Sun.

Imaging the circumstellar disks around newly forming stars is difficult because they can be so dim. It’s harder still when the star itself is lightweight, and the disk is light too. All the disks seen to date have been around Sunlike stars. Until now, the lightest disk was still 7 times more massive than FN Tau.

In FN Tau, the astronomers report that we’re looking at the disk nearly face-on. Its radius is approximately 260 astronomical units (each AU is the distance from the Earth to the Sun). And as disks go, it’s relatively featureless, without any anomalies, rings, spirals, etc. But are there planets lurking in the disk?

Astronomers want to know what kinds of planets could form out of a disk like this. With a lightweight disk to total amount of gravity is much lower. This would make a thicker disk as you get further away from the star. Instead of the Jupiter-like planets turned up in extrasolar planet surveys so far, this environment might actually give a better chance of turning up Earth-mass planets instead.

According to their calculations, this disk should be able to form planets lighter than the Earth within 30 astronomical units of the parent star. The researchers are hoping to make followup observations with a newly commission instrument attached to the Subaru telescope. The HiCIAO will be able to resolve the detailed structure of disks and analyze the size and composition of the dust.

And these observations might help researchers know if FN Tau is a candidate for planetary formation.

Original Source: Subaru Telescope News Release

February 7, 2008December 26, 2015 by Fraser Cain

Deep Impact Begins Searching for Extrasolar Planets

71482main_flyby_w_impactor-516-399.thumbnail.jpg

NASA’s Deep Impact completed its main mission. Back in July 2005, the spacecraft’s impactor carved a hole great big hole out of Comet Tempel 1, helping scientists study what lies beneath its surface. But now its time for the spacecraft to re-enter the space workforce and help discover alien worlds.

NASA recently announced that they had extended Deep Impact’s mission to fly past another comet. This time it’ll be Comet Hartley 2 on October 11, 2010. Just like the previous mission, Deep Impact – now renamed EPOXI – will be studying the surface of the comet with its suite of scientific instruments.

But between now and then, the spacecraft has some time to kill. So astronomers searching for extrasolar planets are calling it into service.

The spacecraft will be focusing its largest telescope at five stars, hoping to catch a glimpse of a planetary transit. This is where a planet dims the light from its parent star as it passes in front.

EPOXI Deputy Principal Investigator Dr. Drake Deming of NASA’s Goddard Space Flight Center in Greenbelt, Md explains the technique:

“When the planet appears next to its star, your telescope captures their combined light. When the planet passes behind its star, your telescope only sees light from the star. By subtracting light from just the star from the combined light, you are left with light from the planet,” said Deming, who is leading the search for exosolar worlds with Deep Impact. “We can analyze this light to discover what the atmospheres of these planets are like.”

This search for extrasolar planets has already begun. Deming and his team directed EPOXI to begin making observations on January 22, 2008. It’s looking at stars which are already known to have transiting planets. The hope is that these stars actually contain multiple planets. Since planets seem to orbit on the same plane, if one passes in front of the star, the rest should too. Even if the planets don’t pass perfectly in front of the star, the spacecraft might be able to detect them from the gravitational influence they have on light coming from the star.

EPOXI will be looking for transiting planets down to the size of Earth, orbiting some of our closest neighboring stars.

Original Source: NASA News Release

January 16, 2008December 26, 2015 by Nancy Houser

Astronomers Could Detect Oceans on Extrasolar Planets

Imagine if astronomers could tell the difference between Earth-like extrasolar planets just by seeing the reflected light from their oceans? That sounds like science fiction, but a team of researchers have proposed that it’s really possible to detect the shape of the light curve glinting off an extrasolar planet and know if it has oceans.

This ground-breaking (water splashing?) idea was written in a recent journal article by D.M. Williams and E. Gaidos, entitled Detecting the Glint of Starlight on the Oceans of Distant Planets published January, 2008 in the Arxiv prepress e-Print archive.

The article describes the methods astronomers could use to detect the glint, or water reflection, from the “disk-averaged signal of an Earth-like planet in crescent phase.” They used the Earth as an example, and generated a series of light curves for a planet with our orientation and axial tilt.

They calculated that planets partially covered by water should appear much brighter when they’re near the crescent phase because light from the parent star reflects off the oceans very efficiently at just the right angles. By watching an extrasolar planet move through its orbit, its light curve should give off the telltale signature that there are oceans present.

According to their calculations, this method should work for about 50% of the visible planets. Furthermore, it should be possible to measure the ratio of land to water, and even get a sense of continents.

In order to test their theories, they’re planning to use remote observations of Earth, using interplanetary spacecraft. This will demonstrate if Earth can be observed at extreme phase anglesâ€”orbiting spacecraft around or on route to Mars.

And then the upcoming planet hunting missions, such as Darwin and the Terrestrial Planet Finder (if it ever gets completed) should be able to make the direct analysis of Earth-sized worlds orbiting other stars. Just by measuring the brightness, they should know if there are oceans, boosting the prospects for life.

Original Source: Arxiv

January 15, 2008December 26, 2015 by Fraser Cain

Using Gravity to Find Planets in the Habitable Zone

Astronomers have several techniques to discover planets. But one of the least used so far, gravitational microlensing, might be just the right technique to find planets in the habitable zone of nearby dwarf stars.

The first way astronomers find planets is with the radial velocity technique. This is where the gravity of a heavy planet yanks its parent star around so that the wobbling motion too and fro can be measured.

The second technique is through transits. This is where a planet dims the light coming from its parent star as it passes in front. By subtracting the light from when the planet isn’t in front of the star, astronomers can even measure its atmosphere.

The third way is through gravitational microlensing. When two stars are perfectly lined up, the closer star acts as a natural lens, brightening the light from the more distant star. Here on Earth, we see a star brighten in a very characteristic way, and then dim down again. A blip in the change of brightness can be attributed to a planet.

Unlike the other two methods, microlensing allows you to reach out and see planets at tremendous distances – even clear across the galaxy. The problem with microlensing is that it’s a one-time opportunity. You’re never going to see those stars line up in just the same way again.

But Rosanne Di Stefano and Christopher Night from the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA think there’s another way microlensing could be used. In their research paper entitled, Discovery and Study ofNearby Habitable Planets with Mesolensing, the researchers propose that many stars have a high probability of becoming a lens.

Instead of watching the sky, hoping to see a lensing event, you watch specific stars and wait for them to pass in front of a more distant star.

These high-probablility lenses are known as mesolenses. By studying a large number of dwarf stars, they expect that many of them should pass in front of a more distant star as often as once a year. And if pick your targets carefully, like dwarf stars moving in front of the Magellanic Clouds, you might get even more opportunities.

Unlike other methods of planet detection, gravitational lensing relies on light from a more distant star. It is therefore important to ask what fraction of nearby dwarfs will pass in front of bright sources and so can be studied with lensing. Within 50 pc, there are approximately 2 dwarf stars, primarily M dwarfs, per square degree.

For less massive red dwarf stars, you should be able to see them at a distance of 30 light years, and for Sun-mass stars out to a distance of 3,000 light years. These stars are close enough that if a planet is detected in the habitable zone, followup techniques should be possible to confirm the discovery.

They calculated that there are approximately 200 dwarf stars passing in front of the Magellanic Clouds right now. And many of these will have lensing events with the stars in the dwarf galaxies.

Instead of monitoring specific stars, previous surveys have just watched tens of millions of stars per night – hoping for any kind of lensing event. Even though 3,500 microlensing candidates have been discovered so far, they tend to be with stars at extreme ranges. Even if there were planets there, they wouldn’t show up in the observations.

But if you pick your stars carefully, and then watch them for lensing events, the researchers believe you should see that brightening on a regular basis. You could even see the same star brighten several times, and make follow-up observations on its planets.

And there’s another advantage. Both the radial velocity and transit methods rely on the planet and star being perfectly lined up from our vantage point. But a microlensing event still works, even if the planetary system is seen face on.

By using this technique, the researchers think that astronomers should turn up lensing events on a regular basis. Some of these stars will have planets, and some of these planets will be in their star’s habitable zone.

Original Source: Arxiv

January 11, 2008December 26, 2015 by Fraser Cain

Red Dwarfs Have Teeny Tiny Habitable Zones

As space telescopes get larger and more sensitive, the search for Earth-sized worlds surrounding other stars is about to get rolling. But astronomers are going to need to know where to look. A team of researchers are working on a survey of nearby stars, calculating the habitable zones around them. When the search begins, astronomers are going to want to study these regions.

The Research Consortium on Nearby Stars (RECONS) is a survey using relatively small telescopes to study the habitable zones in the nearby stars. The team uses measurements of various stars brightnesses at optical and infrared wavelengths matched with their distances to get a sense of the stars’ habitability.

After gathering together a big list of potential candidate stars, the researchers can then categorize stars by size and temperature to find ones that might harbour life.

“Once we have good values for the temperatures and sizes of the nearby stars, we can estimate how hot planets will be at different distances from the stars,” explains Justin Cantrell, a Doctoral Candidate in Astronomy at Georgia State University. “We consider those stars that would have surface temperatures suitable for liquid water to be in the traditional habitable zone.”

The researchers were looking for habitable zones around red dwarf stars, which can be 50-90% smaller than the Sun and much cooler. The comprise 70% of the stars in the Milky Way, but they’re harder to spot because they put out less light.

They were surprised to learn that these red dwarf stars have tiny habitable zones. When they added up the habitable zones of 44 red dwarf stars nearby the Sun, they found they didn’t add up to equal the habitable zone of a single Sun like star.

So even though these red dwarfs are common, they’re not great candidates for life. Earth-type stars would need to be perfectly positioned in their tiny habitable zones to be good candidates for life.

Original Source: Georgia State University News Release