WASHINGTON — Astronomers using NASA’s Spitzer Space Telescope have detected what they believe is a planet two-thirds the size of Earth. The exoplanet candidate, called UCF-1.01, is located a mere 33 light-years away, making it possibly the nearest world to our solar system that is smaller than our home planet. Image credit NASA/JPL-Caltech – Artist Concept
NASA Telescope Joins the Search
Planets orbiting other stars are tough to see. This is largely because planets are tiny, dim points of light and stars — even dimmer, fainter ones, are still much brighter and larger than any nearby worlds. So, the planets are usually lost in the glare. Astronomers have come up with yet another way to find close faint stars that may have planets in orbit around them, using the Galaxy Evolution Explorer satellite (also known as GALEX).
The technique should help in the hunt for planets that lie beyond our solar system, because nearby, hard-to-see stars could very well be home to the easiest-to-see alien planets.
Despite the hundreds of planets discovered by the very successful Kepler Mission (which looks for the effects of a planet’s existence on the light streaming from a star), only a handful of distant planets, or exoplanets, have been directly imaged.
The technique for GALEX involves searching out small, newborn stars — which are less blinding, making the planets easier to see. However, finding those dim newborns is a tough project, too.
Fortunately, such young stars are hot — which means that they emit more ultraviolet light than their older counterparts. This makes them easy to spot by the ultraviolet-sensitive GALEX satellite.
“We’ve discovered a new technique of using ultraviolet light to search for young, low-mass stars near the Earth,” said David Rodriguez, a graduate student of astronomy at UCLA, and lead author of a recent study. “These young stars make excellent targets for future direct imaging of exoplanets.”
Tantrum-Throwing Baby Stars
Young stars, like human children, tend to be a bit unruly — they spout a greater proportion of energetic x-rays and ultraviolet light than more mature stars. In some cases, x-ray surveys can pick out these youngsters due to the “racket” they cause. However, many smaller, less “noisy” baby stars perfect for exoplanet imaging studies have gone undetected except in the most detailed X-ray surveys. To date, such surveys have covered only a small percentage of the sky.
Rodriguez and his team figured the Galaxy Evolution Explorer, which has scanned about three-quarters of the sky in ultraviolet light, could fill this gap. Astronomers compared readings from the telescope with optical and infrared data to look for the telltale signature of rambunctious junior stars. Follow-up observations of 24 candidates identified in this manner determined that 17 of the stars showed clear signs of youth, validating the team’s approach.
“The Galaxy Evolution Explorer can readily select young, low-mass stars that are too faint to turn up in all-sky X-ray surveys, which makes the telescope an incredibly useful tool,” Rodriguez said.
Cool, Red and in the Neighborhood
Astronomers call the low-mass stars in question “M-class” stars. Also known as red dwarfs, these stars glow a relatively cool crimson color compared to the hotter oranges and yellows of stars like our sun, and the whites and blues of the most scorching stars. With data from the Galaxy Evolution Explorer, astronomers could reap a bounty of these red dwarfs still in their cosmic youth, under 100 million years old.
In many ways, these stars represent a best-case scenario for the direct imaging of exoplanets. They are close and in clear lines-of-sight, which generally makes viewing easier. Their low mass means they are dimmer than heavier stars, so their light is less likely to mask the feeble light of a planet. And because they are young stars, their planets are freshly formed, and thus warmer and brighter than older planetary bodies.
The Better to See Planets With
So far, only a handful of the more than 500 exoplanets on record have actually been “seen” by our ground- and space-based telescopes. The vast majority of foreign worlds have instead turned up via indirect means. One common technique, for instance, relies on detecting the slight gravitational “wobbles” exoplanets impart to their host stars. Another technique, the “transit method,” registers the tiny dip in a star’s light as an exoplanet crosses in front of it relative to our vantage point. NASA’s Kepler mission, in just its first four months of operations, has already come up with a list of more than 1,200 candidate exoplanets using the transit method.
At a very basic level, directly imaging an exoplanet is worthwhile because, after all, “seeing is believing,” Rodriguez said. But catching a glimpse of an exoplanet also opens up novel scientific avenues.
Direct imaging is well suited for seeing big planets circling host stars at considerable distances, comparable to Uranus and Neptune in our solar system. Observing such arrangements is useful for testing concepts of solar system evolution, Rodriguez said. Plus, gleaning details about the atmospheres of imaged exoplanets is less difficult than indirectly investigating worlds that transit their stars.
As for actually imaging clouds or surface features of exoplanets, however, that will have to wait. Current images of exoplanets, while full of information, resemble fuzzy dots. But as technology advances, ever more information about our close-by planetary brethren will emerge.
Data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission could also reveal stars that would make good candidates for imaging planets. Its all-sky maps will allow scientists to pick out nearby, young stars surrounded by warm disks of planetary debris that glow with infrared light. Such stars are similar to the ones where planets have already been successfully imaged.
The European Southern Observatory (ESO) announced last week that it had detected an atmospheric storm on a gas giant exoplanet (about 60% the mass of Jupiter) orbiting a star in the constellation Pegasus. The planet is known as HD209458b and is about 150 light years distant from our own solar system. As noted by the team leader Dr. Ignas Snellen: “HD209458b is definitely not a place for the faint-hearted. By studying the poisonous carbon monoxide gas with great accuracy we found evidence for a super wind, blowing at a speed of 5000 to 10 000 km per hour.” Learn more about this gas giant exoplanet online now here.
ESO Astronomers have measured a superstorm for the first time in the atmosphere of an exoplanet, the well-studied “hot Jupiter” HD209458b. The very high-precision
observations of carbon monoxide gas show that it is streaming at enormous speed from the extremely hot day side to the cooler night side of the planet. The observations also allow another exciting “first” — measuring the orbital speed of the exoplanet itself, providing a direct determination of its mass. Read more at http://www.eso.org/public/news/eso1026/
In a paper to be published in Astronomy and Astrophysics, available online now here, astronomers have concluded that exoplanetary moons should be detectable using orbiting satellite telescopes and a technique known as gravitational microlensing. This technique, a refinement of gravitational lensing, applies Einstein’s General Theory of Relativity and its curvature of space effect on the path that the light will follow. Although the technique has only been used to discover a very small percentage of the 430 or so known exoplanets, it apparently may be ultimately used to discover moons orbiting exoplanets, where the other techniques cannot accomplish this feat. The paper is provides the reader an excellent overview of gravitational lensing, gravitational microlensing and its link to the experiments done almost a century ago to first demonstrate that Einstein’s General Theory of Relativity was correct.
Typically astronomers do not have a clear idea of which stars are best candidates for exoplanet searches. Last week in Nature, astronomers with the European Southern Observatory (ESO) announced that they believe they have discovered a proxy for stars that have orbiting planets. As the lead author of the paper, Garik Israelian, states “we have now found that the amount of lithium in Sun-like stars depends on whether or not they have planets.” The ESO announcement released last week is online here, and the Nature article wherein the findings are published are available here.
About 50 light years distant from our own Sun is a star called GJ 758. Astronomers categorize this star as a G9-type star. That means that its surface temperature is a little cooler than our own Sun, which is G2-type star with a surface temperature of 5800 Kelvin. It turns out that GJ 758 has at least one companion (there is evidence of a second), a massive gas giant between 10 and 40 times the mass of Jupiter, perhaps making it a brown dwarf. This extrasolar planet, or exoplanet, is about 29 AU out from GJ 758 about the distance that Neptune or Pluto are from our Sun. You can learn more about the discovery of the companion of GJ 758 online now here.
In 2006, a group of astronomers led by Dr. Swain, published a paper in the journal Nature which got a lot of attention. According to this paper, the team discovered water in the atmosphere of the exoplanet known as HD189733b. Yesterday, another team of astronomers led by Dr. David Sing, made available their results from a similar study of HD189733b. In their paper to be published in Astronomy and Astrophysics, available online now here, Dr. Sing’s group reports that no water was discovered in the atmosphere of HD189733b. This is a good example of the process of science, as well as a means to see how data from what is called transit spectrophotometry, can be used to study exoplanets.
In a paper to appear in Astronomy and Astrophysics, available online now here, astronomers speculate on the nature of one of the most recently discovered exoplanets, known as CoRoT-7b. This exoplanet is estimated to be at least 1.68 times the radius of the Earth. However, it is so close to its star that it takes less than a day for it to complete a single orbit. With better refinements of CoRoT-7b’s mass, and spectral analysis, astronomers hope to understand the nature and composition of the exoplanet. They present one possible view, which can be confirmed with additional observations.