New way to find alien planets

Artist's concept of a red dwarf star and three planets

This artist's concept shows a young, red dwarf star circled by three planets. Such small, dim stars could be ideal targets for astronomers wishing to take images of exoplanets.

  • Planets circling bright stars are hard to see because of the stars’ glare
  • Those that circle dimmer stars could be much easier to image
  • So the hunt is on to find candidate nearby, small, dim stars

ASTRONOMERS HAVE A NEW WAY to identify close, faint stars with NASA’s Galaxy Evolution Explorer satellite.

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.

The glare of bright, shining stars has frustrated most efforts at visualising distant worlds. So far, only a handful of distant planets, or exoplanets, have been directly imaged.

Small, newborn stars are less blinding, making potential orbiting planets easier to see, but the fact that these stars are dim means they are hard to find in the first place.

Fortunately, young stars emit more ultraviolet light than their older counterparts, which makes them conspicuous to the ultraviolet-detecting Galaxy Evolution Explorer.

“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.”

Artist's impression of GALEX

NASA's Galaxy Evolution Explorer could be pressed into service to find faint stars that are home to planets.

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. They 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.

Cool, red, and in the neighbourhood

Astronomers call the low-mass stars in question “M-class” stars. Also known as red dwarfs, these stars glow a relatively cool crimson colour compared to the hotter oranges and yellows of stars like our Sun, and the whites and blues of the most scorching stars.

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.

AB Pictoris and companion

The star AB Pictoris (with most of its glare blocked out) has a tiny companion that is either a brown dwarf star or a massive planet. This is one of only a handful of planet candidates to have its image taken.

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 detection methods.

At a very basic level, directly imaging an exoplanet is worthwhile because, after all, “seeing is believing,” Rodriguez said.

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.

The new study was published in the February issue of The Astrophysical Journal and includes co-authors Mike Bessell (Australian National University), Ben Zuckerman (UCLA), and Joel Kastner (Rochester Institute of Technology).

Adapted from information issued by JPL. Images courtesy of NASA / JPL-Caltech / ESO.

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