Universe Today » Extrasolar Planets

Kepler Mission

Tega Jessa — Fri, 19 Mar 2010 20:08:43 +0000

Artist's rendering of the Kepler Mission (NASA)

One of the biggest questions in astronomy and astrophysics is if there are planets like Earth somewhere beyond our solar system. For the longest time it was impossible to find out for sure. This was for several reasons. First stars are much bigger than planets. Second, stars are much brighter than planets. Because of these to facts it was impossible for telescopes to find planets beyond our solar system. It is like a normal person trying to find to seen an atom beneath someone's show with their naked eye. Then came the Kepler observatory.

Scientist have developed many indirect methods to guess if a star had planets. They could observes a star's motion or see if its light was bent by gravity. These methods were based on the fact that a star with planets would move in a small circle caused by the center of mass of shared star and it planets. With the right instruments and calculations astronomers could determine if a star had planets.

The Kepler observatory is a space observatory that was launched March 9 last year. It had new instrument that would allow for more rapid and efficient discovery of extrasolar planets. It does so by observing the light of stars. The is called the transit method and it is actually quite simple and effective. A star should emit a steady amount of light if it has no planets. However, if a planet were to pass in between it and Earth we would be able to notice a slight dip in the amount of light we observe from the star. The Kepler space observatory does this using a photometer that measures the apparent magnitude of target stars. However there are some drawbacks. The dip in magnitude can be caused by the star itself. For this reason such stars are excluded. Another problem is line of sight. Only a percentage of all stars are observable from earth and an even smaller percentage likely have planets whose orbits are on the same plane as ours. However this still leaves a large number of stars to observe.

The main mission of the Kepler Observatory is to find planets in the habitable zones of stars that might have similar characteristics to Earth. We are able to do this because we can calculate the diameter of found planets from the dip in apparent magnitude caused when they pass in front of their stars. The Kepler mission is expected to last 3.5 years.

If you enjoyed this article there are several others Universe Today that you will enjoy. There is a good article about Kepler's first planet sighting. There is also an interesting article about Kepler being used to measure the size of the Universe.

You can also find great resources online. You can go to NASA's Kepler web site. You can also check out seti.org.

You can also listen Astronomy Cast. Episode 34 talks about looking for other Earths.

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Post tags: Astronomy, Extrasolar Planets, space

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Finally, a "Normal" Exoplanet

Nancy Atkinson — Thu, 18 Mar 2010 23:33:08 +0000

Artist’s impression of Corot-9b. Credit: ESO/L. Calçada

Chalk up another exoplanet discovery for the CoRoT satellite. But this planet, while a gas giant, could have temperatures cool enough to host liquid water. Corot-9b orbits a sun-like star at a distance similar to Mercury – one of the largest orbits of any extrasolar planet yet found, and may have an interior that closely resembles Jupiter and Saturn. “This is a normal, temperate exoplanet just like dozens we already know, but this is the first whose properties we can study in depth,” said Claire Moutou, who is part of the international team of 60 astronomers that made the discovery. “It is bound to become a Rosetta stone in exoplanet research.”
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Ripped to Shreds, Exoplanet Suffers Painful Death

Jean Tate — Thu, 25 Feb 2010 18:09:26 +0000

Illustration of WASP-12b in orbit about its host star (Credit: ESA/C Carreau)

WASP-12b, discovered in 2008, is a real outlier among the 400 or so exoplanets discovered to date. Not that it's particularly massive (it's a gas giant, not unlike Jupiter), nor that its homesun (host star) is particularly unusual (it's rather similar to our own Sun), but it orbits very close to its homesun, and is considerably larger than any other gas giant discovered to date.

Results from recent research explain why WASP-12b is so unusual; we're watching it die a painful death at the hands of its homesun, which is snacking on it.
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© Jean Tate for Universe Today, 2010. | Permalink | 5 comments | Add to del.icio.us
Post tags: Extrasolar Planets, Super Earths, tidal energy, tidal forces

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Astronomers Find Youngest Exoplanet Yet

Nancy Atkinson — Thu, 18 Feb 2010 22:25:40 +0000

Artist's impression of BD+20 1790b, the youngest exoplanet yet discovered. Credit: M. Hernon Obispo

Overcoming interference from a very active young sun-like star, a group of astronomers were able to find what they determined is the youngest exoplanet yet discovered. BD+20 1790b is 35 million years old (Earth is about 100 times older at 4.5 billion years) and is located about 83 light years away from our planet. Previously, the youngest known exoplanet was about 100 million years old. Studying this planet will help our understanding of planetary evolution.
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Armazones Chile to be the Site for the 42 meter European Extremely Large Telescope?

Jean Tate — Fri, 12 Feb 2010 21:18:54 +0000

Question: Where are the night skies always dark, cloud-free 360 days a year, bone-dry, and orbiting 3.5 km above sea level?
Answer: Armazones Mountain, Atacama desert, Chile.
Question: Who wants to go live there?
Answer: The European Extremely-Large Telescope (E-ELT)!

"We are talking about the biggest telescope in the world, the biggest for a long time to come. That means we have to choose the best spot. Chile has a superb location. It's the best in the world, there's no doubt," the European Southern Observatory's astronomer, Massimo Tarenghi, told AFP. He is one of four astronomers – two Chileans, an Italian (Tarenghi) and a German – who were in the desert this week to evaluate its suitability compared to the main other contender: the Spanish isle of La Palma in the Canary Islands off western Africa.
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© Jean Tate for Universe Today, 2010. | Permalink | 21 comments | Add to del.icio.us
Post tags: chile, ESO, Extrasolar Planets, telescope

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New Technique to Find Earth-like Exoplanets

Nancy Atkinson — Wed, 03 Feb 2010 20:39:00 +0000

The Artists impression of HD 189733b, graph and image of the telescope Credit: NASA

Another technique has been added to the exo-planet hunters' toolkit, and it doesn't require huge ground-based telescopes or space-based observatories. A group of astronomers developed the new technique by using a relatively small Earth-based infrared telescope to identify an organic molecule in the atmosphere of a Jupiter-sized planet nearly 63 light-years away. This new ground-based technique will enable the study of atmospheres of planets outside our Solar System, accelerating our search for Earth-like planets with life-related molecules.
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Post tags: Extrasolar Planets, HD 189733b, Infrared Astronomy

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First Direct Spectrum of an Exoplanet Orbiting a Sun-like Star

Nancy Atkinson — Wed, 13 Jan 2010 11:10:46 +0000

Image of the HR 8799 system. Image credit: MPIA / W. Brandner

Astronomers have obtained the first direct spectrum – a “chemical fingerprint” – of a planet orbiting a distant, Sun-like star, providing direct data about the composition of the planet's atmosphere. An international team of researchers studied the planetary system around HR 8799 a bright, young star with 1.5 times the mass of our Sun, and focused on one of three planets orbiting the star. While the results were unusual and pose a challenge to current models of the exoplanet's atmosphere, the accomplishment represents a milestone in the search for life elsewhere in the Universe.
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Second Smallest Exoplanet Found

Nancy Atkinson — Thu, 07 Jan 2010 22:28:05 +0000

This artists' rendition shows a super-Earth, or low mass exoplanet, orbiting close to its parent star. Credit: L. Calcada

Planet hunters have detected an extrasolar planet that is only four times the mass of Earth, making it the second smallest exoplanet ever discovered. Astronomers using the 10-meter Keck I telescope at the Keck Observatory in Hawaii found the un-poetically named HD156668b, which has a mass of roughly 4.15 Earth masses. It orbits its parent star in just over four days and is located roughly 80 light years from Earth in the direction of the constellation Hercules. This adds to the growing list of so-called "Super-Earths" now being found.
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© nancy for Universe Today, 2010. | Permalink | 8 comments | Add to del.icio.us
Post tags: Extrasolar Planets, Super Earths

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Planet Formation Observed Around Massive Stars

Steve Nerlich — Wed, 06 Jan 2010 16:15:20 +0000

As the old saying goes – big stars live fast and die young. And, according to new research presented at the 215^th meeting of the American Astronomical Society, so do their planets.(...)
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Kepler Discovers Planets-like Objects Hotter Than Stars

Nancy Atkinson — Mon, 04 Jan 2010 15:12:09 +0000

Possible habitable zones around stars. Credit: Kepler mission

The Kepler mission announced the discovery of 5 new extrasolar planets today at the American Astronomical Society meeting in Washington, DC, each with some very unusual properties. But additionally, the space telescope has spotted some Jupiter-sized objects orbiting stars, and these objects are hotter than the host star. The science team has no idea what these objects could be, but they are part of 100 planetary candidates Kepler has observed that are still being analyzed.
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First Super-Earths Discovered Around Sun-like Stars

Nancy Atkinson — Mon, 14 Dec 2009 17:25:42 +0000

Astronomers say it’s a "neck-and-neck race" as to whether the first potentially habitable planets will be detected from the ground or from space, and today an international team of planet hunters announced they have discovered as many as six low-mass planets around two nearby Sun-like stars, using two ground-based observatories. This haul of planets includes two "super-Earths" with masses 5 and 7.5 times the mass of Earth.
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Exoplanet Not Really There?

Nancy Atkinson — Tue, 08 Dec 2009 22:55:13 +0000

This artist's concept shows the smallest star known to host a planet. Image credit: NASA/JPL-Caltech

In May 2009, astronomers were jubilant: finally, an extra solar planet had been found by using the method of astrometry. That's great, except, they may not have found a planet after all. Researchers from JPL reported they found a Jupiter-like planet around a star smaller than our sun. But follow-up observations of the star VB10 are coming up empty. "The planet is not there," said Jacob Bean from the Georg-August University in Gottingen, Germany, who used a different and more successful approach to look for exoplanets, radial velocity.
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Exobiology

Jean Tate — Fri, 04 Dec 2009 18:36:34 +0000

Exobiology (same thing as astrobiology) is about life in space (on other planets, and moons; in other solar systems): where it is, what it is, how it started, and how it evolved (all studied scientifically, of course). Because the origin of life right here on Earth, and its early evolution, is essentially unknown, and because of the distinct possibility of similiarities with the origin (and early evolution) of life elsewhere in the universe, exobiology includes research into abiogenesis (and early, and extreme, life on Earth).

Exobiology is very much a multi-disciplinary field, drawing on biology, chemistry, geology (and planetary science), physics, and astronomy.

Because we have a sample of just one – life on Earth – it is difficult to make anything but the most general decisions on what lines of exobiology research are likely to be productive (keep in mind that null results can, of course, be quite productive). Conservatively, looking for planets like Earth in orbit around stars like the Sun (in age as well as mass, metallicity, etc), and looking for clues for fossil life in planetary environments like those found today on Earth (e.g. early Mars) seem better options than investigating possible silicon-based life (to take just one example).

As the number of exosolar (or extrasolar) planetary systems known continues to grow, quickly, discovering the prevalence of Earth-mass planets, in goldilocks orbital zones, seems like a good idea … so today we have the Kepler mission and COROT.

As the early Mars becomes better understood – and the widespread distribution of liquid water then – so today we have plans for the Mars Science Laboratory and ExoMars (the discovery of methane in the Martian atmosphere certainly spurs such developments).

Less conservatively, the discovery of life around black smokers and sites like Lost City (not to mention entire ecosystems within crustal rocks … several km beneath the surface) sparked interest in the possibility of life in Europa, on Titan, even Enceladus (life – albeit rather simple life – we now know does not need to depend, ultimately, on the Sun's (or another star's) radiant energy … think chemolithoautotrophs).

Did you know that NASA has an exobiology branch? Check it out! Duke University's Chemistry Department has an interesting Introduction to Exobiology you might find interesting too.

Universe Today stories on exobiology? Yep, lots; here's a random selection: Martian Explorers Should Be Looking for Fossils, Did Life Arrive Before the Solar System Even Formed?, Extremophile Hunt Begins in Antarctica, Implications for Exobiologists , and New Targets to Search for Life on Europa.

Any Astronomy Cast episodes on exobiology? Yep … but it's called Astrobiology.

© Jean Tate for Universe Today, 2009. | Permalink | No comment | Add to del.icio.us
Post tags: Extrasolar Planets, life in the universe, life on mars, life on other planets

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Cool – Literally – Extrasolar Planet Imaged

Nicholos Wethington — Thu, 03 Dec 2009 22:14:01 +0000

Yet another planet outside of our Solar System has been directly imaged, bumping the list up past ten. Given that the first visible light image of an extrasolar planet was taken a little more than a year ago, the list is growing pretty fast. The newest one, planet GJ 758 B is also the coolest directly imaged planet, measuring 600 degrees Kelvin, and it orbits a star that is much like our own Sun. GJ 758 B has a mass of between 10-40 times that of Jupiter, making it either a really big planet or a small brown dwarf.(...)
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Post tags: adaptive optics, Extrasolar Planets

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Hot Jupiters Bully Super Earths

Jon Voisey — Mon, 23 Nov 2009 18:20:43 +0000

Bullies are everywhere and the universe is no exception. In our own solar system, Jupiter's mass is second only to that of the Sun. Its gravitational effects tug around a set of asteroids known as the Trojans and may prevent the asteroid belt from becoming anything more substantial. Fortunately, our humble planet gets along with this gravitational monstrosity, but it didn't have to be so. What could such massive menaces do to planets like Earth in newly forming solar systems?(...)
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Post tags: Extrasolar Planets, hot jupiter, super earth

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Shedding Light on the Sun's "Lithium Mystery"

Nancy Atkinson — Wed, 11 Nov 2009 20:31:30 +0000

For decades, astronomers have known our Sun contains a low amount of lithium, while other solar-like stars actually have more. But they didn't know why. By looking at stars similar to the Sun to study this anomaly, scientists have now discovered of a trend: the majority of stars hosting planets possess less than 1% of the amount of lithium shown by most of the other stars. “The explanation of this 60 year-long puzzle is for us rather simple,” said Garik Israelian, lead author on a paper appearing in this week's edition of Nature. “The Sun lacks lithium because it has planets.”

This finding sheds light not only on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems.
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Multi-Planet System is Chaotic, Dusty

Nancy Atkinson — Wed, 04 Nov 2009 21:27:36 +0000

NASA's Spitzer Space Telescope captured this infrared image of a giant halo of very fine dust around the young star HR 8799. Image credit: NASA/JPL-Caltech/Univ. of Ariz.

Just what is going on over at the star HR 8799? The place is a mess! But we can just blame it on the kids. Young, hyperactive planets circling the star are thought to be disturbing smaller comet-like bodies, causing them to collide and kick up a huge halo of dust. HR 8799 was in the news in November 2008, for being one of the first with imaged planets. Now, NASA's Spitzer Space Telescope has taken a closer look at this planetary system and found it to be a very active, chaotic and dusty system. Ah, youth: our solar system was likely in a similar mess before our planets found their way to the stable orbits they circle in today.
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© nancy for Universe Today, 2009. | Permalink | 2 comments | Add to del.icio.us
Post tags: Extrasolar Planets, Spitzer Space Telescope

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No Earth-Sized Planet Hunting for Kepler Until 2011

Nancy Atkinson — Mon, 02 Nov 2009 16:25:48 +0000

Artist concept of Kepler in space. Credit: NASA/JPL

A glitch in the Kepler spacecraft's electronics means the space telescope will not have the ability to spot an Earth-sized planet until 2011, according to principal investigator William Borucki. Noisy amplifiers are creating noise that compromises Kepler's view, and the team will have to generate and upload a software fix for the spacecraft. "We're not going to be able to find Earth-size planets in the habitable zone — or it's going to be very difficult — until that work gets done," said Borucki, who revealed the problem last week to the NASA Advisory Council.
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Organic Molecules Detected in Exoplanet Atmosphere

Nancy Atkinson — Tue, 20 Oct 2009 16:10:24 +0000

Artist concept of exoplanet HD 209458b. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

The basic chemistry for life has been detected the atmosphere of a second hot gas planet, HD 209458b. Data from the Hubble and Spitzer Space Telescopes provided spectral observations that revealed molecules of carbon dioxide, methane and water vapor in the planet's atmosphere. The Jupiter-sized planet – which occupies a tight, 3.5-day orbit around a sun-like star — is not habitable but it has the same chemistry that, if found around a rocky planet in the future, could indicate the presence of life. Astronomers are excited about the detection, as it shows the potential of being able to characterize planets where life could exist.
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© nancy for Universe Today, 2009. | Permalink | 8 comments | Add to del.icio.us
Post tags: Astrobiology, Extrasolar Planets

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HARPS Discovers 32 New Exoplanets

Nancy Atkinson — Mon, 19 Oct 2009 13:44:39 +0000

A planet 6 times the mass of Earth orbits around the star Gliese 667 C, which belongs to a triple system. Credit: ESO

Astronomers have found 32 new planets outside our solar system with the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for the European Southern Observatory's (ESO) 3.6-metre telescope. The number of known exoplanets is now at 406, and HARPS itself has discovered more than 75 exoplanets in 30 different planetary systems. Included in this most recent batch are several low-mass planets – so-called "Super Earths" about the size of Neptune. The image above is an artist's impression of a planet discovered that is 6 times the mass of Earth, which circles the low-mass host star, Gliese 667 C, at a distance equal to only 1/20th of the Earth-Sun distance. Two other planets were discovered previously around this star.

"HARPS is a unique, extremely high precision instrument that is ideal for discovering alien worlds," said ESO astronomer Stéphane Udry. “We have now completed our initial five-year program, which has succeeded well beyond our expectations.”
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Exoplanet

Jean Tate — Wed, 14 Oct 2009 03:12:51 +0000

Hubbles view of the exoplanet Fomalhaut b (NASA/HST)

An exoplanet – or extrasolar planet – is a planet which orbits a star other than our own Sun.

After a bit of a false start – lasting many decades! – when a small number of detections of planets around other stars were reported but not confirmed, the first reliable, independently confirmed exoplanet was discovered – by Campbell, Walker, and Yang – in 1988 (though solid confirmation came only in 2003), around Gamma Cephei. Between 1988 and 2003, two planets were detected, and confirmed, orbiting a pulsar (which has the catchy name of PSR 1257+12) – in 1992 – and an exoplanet was discovered, and confirmed, around the ordinary (main sequence) star 51 Pegasi (in 1995). It was this discovery that started the modern exoplanet gold rush.

There are now nearly 400 exoplanets detected and confirmed (and a few more whose status is uncertain). The Extrasolar Planets Encyclopaedia is a website which keeps track of all announcements, confirmations, etc. It also has an excellent tutorial on the methods used to discover such planets.

The first multiple system – a star with more than one exoplanet – discovered was Upsilon Andromedae (this star is actually a binary, so the discovery was a first in two ways). The first planet was discovered in 1996, and the second (and third!) in 1999. In this case independent confirmation came quite quickly. Today more than 20 such multiple-planet systems are known.

Most exoplanets have been discovered by the radial velocity, or Doppler, method: the star's apparent speed away from (or towards) us – as measured by sensitive spectrographs – varies in a regular way, due to the gravitational pull of the exoplanet (remember that two bodies in a stable gravitational system will orbit the center of mass). Almost all have been found by ground-based telescopes. This is likely to change in the next few years as dedicated space-based telescopes – such as NASA's Kepler and the ESA's COROT – continue to make new discoveries. As these use the transit method (detecting tiny changes in a star's intensity, as an exoplanet goes between it and us), the Doppler method may soon lose its 'most exoplanets discovered' status.

There are literally dozens of Universe Today stories on exoplanets! Here are a few, covering many different aspects: Smallest Terrestrial Exoplanet Yet Detected, Astrometry Finds an Exoplanet, Exoplanet Has Oddball Orbit, New Technique Allows Astronomers to Discover Exoplanets in Old Hubble Images, Carbon Dioxide Detected on Exoplanet HD 189733 b, and Exoplanet Image Confirmed.

There's also a great overview of this topic in the Astronomy Cast episode A Zoo of Extrasolar Planets, and the somewhat older episode Discovering Another Earth is excellent too.

© Jean Tate for Universe Today, 2009. | Permalink | No comment | Add to del.icio.us
Post tags: extrasolar planet, Extrasolar Planets

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Rocky World COROT-7b Rains Rocks

Nancy Atkinson — Thu, 01 Oct 2009 22:56:37 +0000

The exoplanet Corot-7b is so close to its Sun-like host star that it must experience extreme conditions. Sister planet, CoRot-7c is seen in the distance. Credit: ESO

If any creature lives on COROT-7b, the recently confirmed rocky exoplanet, they might think the sky is falling. This planet is close enough to its star that its "day-face" is hot enough to melt rock, and according to models by scientists at Washington University in St. Louis, COROT-7b's atmosphere is made up of the ingredients of rocks and when "a front moves in," pebbles condense out of the air and rain into lakes of molten lava below. Yikes!
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Super Earths

Fraser Cain — Wed, 09 Sep 2009 19:08:40 +0000

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra.

The holy grail in the search for extrasolar planets will be the discovery of Earthlike planets orbiting other stars. With better telescopes and techniques, astronomers will eventually be able to even detect the atmospheres of extrasolar planets and determine if there's life there. Although Earth-sized planets are impossible to detect with current observatories, astronomers are now finding super earths.

A super Earth is a terrestrial planet orbiting a distant star. But instead of having the mass of our own planet, it might have 2, 5, or even 10 times the mass of the Earth. Although that makes them large, very massive planets, they're not as large or massive as gas giants.

And just because they're called super Earths doesn't mean they're habitable, or even Earthlike in climate at all. Super Earths could be orbiting close to their parent star, or well outside the solar system's habitable zone.

Scientists haven't completely settled on a definition for super Earths. Some believe a planet should be considered a super Earth if it's a terrestrial planet between 1 and 10 Earth masses, while others think it should be between 5 and 10 Earth masses.

The first super Earth ever discovered was found in 1991 orbiting a pulsar. Obviously that wouldn't really be a very habitable place to live. The first super earth found orbiting a main sequence star was found in 2005, orbiting the star Gliese 876. It's estimated to have 7.5 times the mass of the Earth, and orbits its parent star every 2 days. With such a short orbital period, you can expect that it's orbiting very close to its parent star. Temperatures on the surface of the planet reach 650 kelvin.

The first super earth found within its star' habitable zone was Gliese 581 c. It's estimated to have 5 Earth masses, and orbits its parent star at a distance of 0.073 astronomical units (1 AU is the average distance from the Earth to the Sun). That's pretty close to the star, and Gliese 581 c would probably have a runaway greenhouse effect, similar to Venus. But right beside that is Gliese 581 d, with a mass of 7.7 Earths and an orbit of 0.22 AU. This planet could very well have liquid water on its surface.

The smallest super Earth discovered so far is MOA-2007-BLG-192Lb, which has only 3.3 times the mass of the Earth, and was orbiting a brown dwarf star. But this record will probably be beaten by the time you read this, as planet hunters get better. It's only a matter of time before a true Earthlike planet is discovered.

We have written many articles about super Earths. Here's an article speculating on the kinds of atmospheres that super Earths might have, and another article about how similar super Earths really are to our own planet.

Here's an artist's impression of a super Earth features on NASA's Astronomy Picture of the Day website, and here's an article from NASA about super Earths.

We also recorded an episode of Astronomy Cast dealing with the different kinds of extrasolar planets you can find. Listen to it here. Episode 125: A Zoo of Extrasolar Planets.

© Fraser for Universe Today, 2009. | Permalink | No comment | Add to del.icio.us
Post tags: Earth, extrasolar planet, Extrasolar Planets, gliese 581, habitable planets, super earth

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Extrasolar Planets

Abby Cessna — Wed, 09 Sep 2009 18:31:35 +0000

gemini-extrasolar-planet

An extrasolar planet, also called an exoplanet, is a planet that is in a Solar System other than our own. Our Solar System is only one among billions and many of them most likely have planets. As of early this year, 429 extrasolar planets had been discovered. The first extrasolar planets were not discovered until 1992, although astronomers had suspected they existed as far back as the 1500’s when the astronomer Giordano Bruno suggested that there were other solar systems with their own planets. Some astronomers also believed they had identified a couple extrasolar planets in the late 1980’s, but scientists were unable to confirm their existence until later. One reason why extrasolar planets are so difficult to detect is because they are even fainter than the stars. Additionally, the stars also give off light that “washes” the planets out.

One thing that astronomers have been particularly focused on is finding exoplanets that may support life. So far, they have found a number of planets in the habitable zone, which is a theoretical region of space a certain distance from a sun believed to be at the optimum position for supporting life. Earth is in our Solar System’s habitable zone. Most of the extrasolar planets that have been discovered so far are gas giants similar to Jupiter. This is also true for the extrasolar planets discovered in the habitable zone of other stars. However, that does not mean that there are more large extrasolar planets than there are ones similar to the size of Earth. Jupiter-sized planets are simply easier to find because they are much larger. Some astronomers believe that there are actually more Earth-sized exoplanets and that it will simply take more time to find them. In recent years, they have begun to discover smaller extrasolar planets. One of these, HD156668b, was discovered recently orbiting a star located in the region of the Hercules constellation. HD156668b is only a little more than four times the mass of Earth.

Scientists have even discovered what they think are exoplanets that do not orbit a star. Messier22 is a globular cluster with thousands of stars in it. Using the Hubble telescope, astronomers were able to discover that there are some planet-sized objects in the region which do not orbit any stars. These objects appear to be smaller than Jupiter, but approximately 80 times the size of Earth. Astronomers are still trying to figure exactly what these objects are and how they could exist.

Universe Today has articles on the second smallest exoplanet found and planet formation observed around massive stars.

You should also take a look at the top ten exoplanets and catalogue of exoplanets.

Astronomy Cast has an episode on in search of other worlds.

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Post tags: exoplanets, Extrasolar Planets

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Biggest Exoplanet Yet Orbits the Wrong Way

Nancy Atkinson — Wed, 12 Aug 2009 14:07:13 +0000

Credit: KASI/CBNU/ARCSEC." title="Artist's impression of two close extra-solar planets.
Credit: KASI/CBNU/ARCSEC." width="580" height="580" class="size-full wp-image-37309" />

Artist's impression of two close extra-solar planets.
Credit: KASI/CBNU/ARCSEC.

Planet hunters from the UK have discovered the largest exoplanet yet, and its uniqueness doesn't end there. Dubbed WASP-17, this extra large world is twice the size of Jupiter but is super-lightweight, "as dense as expanded polystyrene" one astronomer said. Plus it is going the wrong way around its home sun, making it the first exoplanet known to have a retrograde orbit. As a likely a victim of planetary billiards, astronomers say this unusual planet casts new light on how planetary systems form and evolve.
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