Identifying atmospheres around exoplanets

How Well Can Astronomers Study Exoplanet Atmospheres? (Universe Today) 

At this point, how well can astronomers study the atmosphere around an exoplanet? 

Currently, there are only a handful of methods researchers can use to make estimates of exoplanet atmospheres. Interestingly enough, one method makes use of the light coming from the host star. The basic principle is that the light from a star can be analyzed both before and after an exoplanet crosses in front of the star. By comparing the spectrum from the host star, and the spectrum of an exoplanet, the tell-tale signs of atmospheric contents can be detected.

Kepler discovers 26 planets in 11 systems, speeds up discovery of exoplanets

Credit: NASA Ames/Dan Fabrycky, UC Santa Cruz

Kepler is at it again with 26 confirmed planets. As expected, when you have a telescope with 2300+ candidate discoveries there's going to be a lot of confirmations... From NASA's Kepler website:

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits." 

2012 will be a fun year to watch and I'm positive the 1000 number will be breached. Because Kepler is still a relatively young mission, it will take considerable time before planets with wide orbits (and longer periods between transits) will be detected--but I expect a lot of future detections there as well.

NASA's Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets. These discoveries nearly double the number of verified Kepler planets and triple the number of stars known to have more than one planet that transits, or passes in front of, its host star. Such systems will help astronomers better understand how planets form. 

The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen of them are between Earth and Neptune in size, and further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune. The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun.

NASA's Kepler Announces 11 Planetary Systems Hosting 26 Planets

Scientific American: if planets can form somewhere, they will

Credit: Scientific American/NASA/Ames/JPL-Caltech

Scientific American summarizes our changing views of the universe thanks to the past two decades of extrasolar planet discovery.

Planets in habitable zones, planets orbiting twin suns, miniature solar systems, rogue planets, planets, planets, planets. If there is one single piece of information you should take away from the recent flood of incredible exoplanetary discoveries it is this: Our universe makes planets with extraordinary efficiency – if planets can form somewhere, they will.

We’ve been sidling up on this fact for some time now, but it’s still a remarkable thing to acknowledge. Ten to fifteen years ago, as the first exoplanet detections began to come in, we understood that what we were seeing was potentially just the tip of the iceberg. These were massive objects (Jupiter sized or greater) and most of them were orbiting much closer to their parent stars than any equivalent giant planet in our solar system – hence the ‘hot Jupiter‘ moniker that is still used today. Statistics improved, as did our understanding of how detection techniques were biased towards finding these types of planets (owing to their greater gravitational influence on their parent stars), and estimates were made that suggested only a few percent of normal stars harbored such worlds.

An Abundance of Exoplanets Changes our Universe (Scientific American)

Paper on direct imaging of exoplanets

Some takeaways on direct imaging of exoplanets from a scientific paper at arXiv:

Extra-solar planets or candidates as close to their host star as the Solar System planets (within
30 AU) are still very rare with β Pic b, HR 8799 e, PZ Tel B/b, and HR 8799 d being the only exceptions at 8.5, 14.3, 18.3, and 24.2 AU, respectively, all nearby young stars (19 to 52 pc). As far as angular separation is concerned, the closest planets or candidates imaged directly are PZ Tel B/b, HR 8799 e, β Pic b, HR 8799 d, and GQ Lup b with separations from 0.36 to 0.75 arc sec. 

New AO imaging techniques like ADI, SAM, and locally optimized combination of images
have improved the ability to detect such planets. Future AO instruments at 8-meter ground-based telescopes will improve the accessible dynamic range even further. Imaging with a new space based telescope like JWST (Beichman et al., 2010) or AO imaging at an extremely large telescope of 30 to 40 meters would improve the situation significantly. Imaging detection of planets with much lower masses, like e.g. Earth-mass planets, might be possible with a space-based interferometer like Darwin or TPF, but also only around very nearby stars.

Direct Imaging of Extra-solar Planets - Homogeneous Comparison of Detected Planets and Candidates (via @AllPlanets)

Public planet hunting goes live on BBC, participant discovers planet

As long as I can name my own planets, I want in! Following previous news that Planethunters.org gets +1million classifications, the BBC reports:

The public push initiated on BBC Two's Stargazing Live series to find planets beyond our Solar System has had an immediate result.

A viewer who answered the call has helped spot a world that appears to be circling a star dubbed SPH10066540.

The planet is described as being similar in size to our Neptune and circles its parent every 90 days.

Chris Holmes from Peterborough found it by looking through time-lapsed images of stars on Planethunters.org.

The website hosts data gathered by Nasa's Kepler space telescope, and asks volunteers to sift the information for anything unusual that might have been missed in a computer search.

"I've never had a telescope. I've had a passing interest in where things are in the sky, but never had any more knowledge about it than that," Mr Holmes told BBC News.

"Being involved in a project like this and actually being the one to find something is a very exciting position."

Chris Lintott from Oxford University who helps organise Planethunters.org added: "We're ecstatic. We've been groaning under the strain of all these people who want to help us, which is exactly how it should be."

The public participation project was launched last year, but it got a huge fillip when it was featured in the popular Stargazing series' return to BBC Two on Monday.

Volunteers have tripled to more than 100,000 people, and the number of images inspected has now reached a million.

Stargazing viewer in planet coup

Exoplanets have sunsets too, although their color might be a bit offsetting

Ever wondered what a sunset (or rather, starset) will look like on an exoplanet? A new website, exoclimes.com, has been launched that "is devoted to discussion around the study of planetary atmospheres outside the Solar System":

Extrasolar planets orbit stars, in a similar way to the Earth orbiting the Sun. Professor Frédéric Pont of the University of Exeter has used the extrasolar planets' 'transmission spectrum', taken by the Hubble Space Telescope, to work out the colour of the 'sunsets' created by these stars.

Writing on the website exoclimes.com, where he has posted the two sunset images he has produced, Professor Pont said:  "Unlike its sister planet HD '189, the planet HD '209 ('Osiris') has a sunset that looks truly alien. The star is white outside the atmosphere, since its temperature is close to that of the Sun. It then acquires a bluish tinge as it sinks deeper, because the absorption by the broad wings of the neutral sodium lines (the spectral lines responsible for the gloomy orange of sodium street lighting) remove the red and orange from the star light.

"One key difference with a sunset on Earth is that the 'sun' is much larger from '209, because the planet is very close. Instead of changing colour as it moves near the horizon, the host star spans all colours at once."

The Science of Sunsets

Planethunters.org gets +1million classifications

Thanks to your help and BBC Stargazing, we managed 1,084,760 classifications in 48 hours. 

There's still more to do, and more discoveries to be made, so keep clicking!

As written on planethunters.org (via prof. Brian Cox, everyone's favourite astrophysicist).

Video showing radius, orbit and surface temperature of candidate exoplanets

This video has been around but I'm only coming across it now, via NASA--beautiful!


Kepler Exoplanet Candidates from blprnt on Vimeo.

As far as I can tell, this video is based on the February 2011 batch of KOIs; I wonder what it will look like using the updated KOI database (containing ±1000 more candidates).

Gaia: using astrometry to discover extrasolar planets

To date, most extrasolar planets have been discovered using the radial velocity method, where a periodic shift of a star's spectrum betrays a planetary companion. Up and coming is the transit method, used by the Kepler spacecraft to detect exoplanets passing in front of their parent stars.

Even though it's still behind radial velocity in terms of planets discovered, this method is playing catch-up fast: there are already thousands of KOIs (Kepler Object of Interest), or exoplanet candidates detected by Kepler that await confirmation using other methods.

From 2013, the Gaia spacecraft could potentially shift the balance to astrometry as a major planet discovery method. Its mission is to determine star's positions on a scale much more detailed than is possible from Earth, thereby creating a 3-dimensional map of the Galaxy. If a star has a big enough planet, it will wobble and therefore periodically change it's position in the sky. In this ESA presentation from November 2010 (PPT), it is claimed that Gaia could detect planets down to 10 Earth masses:

Results expected:

~2000 exo-planets (single systems)

~300 multi-planet systems

displacement for 47 UMa = 360 μas

orbits for ~1000 systems

masses down to 10 MEarth to 10 pc

Will 2012 be the year of Earth sized exoplanets? Trend says yes

The graph on the right (from Exoplanets.eu) is a simple correlation plot, graphing planet mass against year of discovery*. Apart from 1992 (when 3 planets were discovered around a pulsar), the lower bound on exoplanet mass seems to decrease every year.

If this trend continues, we might see a number of exciting discoveries in 2012; after all, the lower a planet's mass, the more it resembles Earth (in rough terms). Actually, the party has already started with the discovery of 3 sub-earth sized planets last week.

If 2011 was the year of super-earths, then will 2012 be the year of Earth sized exoplanets?

*Note that only sub-Jupiter-sized planets are shown.

Goldilocks moons around binary stars

Universe Today has an interesting article up about the possibility of so-called Goldilocks moons (i.e. moons that are conducive to life) around extrasolar planets that are themselves not habitable.

Kepler 16b’s roughly circular orbit, about 65 million miles from the stars, is on the outer edge of this habitable zone. Being a gas giant, 16b is not a habitable terrestrial planet. However, an Earth-like moon, a Goldilocks Moon, in orbit around this planet could sustain life if it were massive enough to retain an Earth-like atmosphere. “We determined that a habitable exomoon is possible in orbit around Kepler-16b,” Quarles said.

Discovery of planets in binary star systems

KBPS reports:

San Diego State University astronomers, along with a team of scientists, have discovered two more planetary systems with two suns. Before, it was believed planets could only orbit a single sun, because a double sun, also known as a double star, would make the system too chaotic.

Since about half of the star systems in our galaxy contain one or more stars, this finding significantly increases the potential number of exoplanets.

Cumulative exoplanet count since 1989

Since 1989*, hundreds of extrasolar planets have been discovered and there's a massive back catalog of unconfirmed planets. Given the enormous improvements in detection methods, the growth of the scientific field itself (more 'eyes on lenses'), and sheer amount of stars in our universe, we can expect to see more and more planets discovered every year. Using data from the Extrasolar Planet Encyclopaedia, this is the cumulative exoplanet count so far:

If this exponential trend continues in 2012, we may see the 1000 count by the end of the year!

(*First exoplanet was discovered in 1989 but only confirmed in 2003; the real excitement didn't start until 1995)

100 billion planets a conservative estimate for our galaxy

Planets around other stars are much more common than previously thought, according to scientists. The  Wall Street Journal reports:

Astronomers said Wednesday that each of the 100 billion stars in the Milky Way probably has at least one companion planet, on average, adding credence to the notion that planets are as common in the cosmos as grains of sand on the beach.

They used gravitational microlensing on millions of potential host stars. So far, only a handful of planets have been detected using this method.

By their calculations, most of the Milky Way's stars—100 billion is the most conservative estimate—have one or more planets, the researchers reported in Nature Wednesday. None of the planets detected so far appear suitable for conventional carbon-based life as known on Earth.

Almost two-thirds of the stars likely host a planet measuring about five times Earth's mass, and half of them harbor a planet about the mass of Neptune, which is 17 times the mass of Earth. About one-fifth of them are home to a gas giant like Jupiter or a still more massive planet.

"One can point at almost any random star and say there are planets orbiting that star," said astronomer Uffe Grae Jorgensen, of the University of Copenhagen in Denmark, a member of Dr. Cassan's team.