The planet-hunting TESS telescope has big shoes to fill — shoes that once belonged to Kepler. Before its
retirement last October, the pioneering Kepler Space Telescope spent 10 years paving the way for the search for planets (and possibly life) outside the solar system. Of the
nearly 4,000 exoplanets discovered around other stars to date, Kepler found more than half. But now,
TESS is up to bat. And it's already off to a great start.
Over the next two years, TESS is expected to find roughly 20,000 new exoplanets hiding in the glow of the sky's brightest stars. Additionally, according to
NASA's exoplanet exploration website, "TESS will discover dozens of Earth-sized planets and up to 500 planets less than twice the size of Earth." But what about the even smaller stuff? For instance, exocomets.
Well, don't fret. TESS can find those too.
According to a new study, astronomers have detected an exocomet passing in front of one of the sky's brightest stars,
Beta Pictoris, located some 65 light-years away. Although other exocomets (and an
exoplanet) have been detected around Beta Pic before, this is the first time astronomers have found a comet around the star using a light curve from TESS.
"Other astronomers have seen hints of exocomets towards Beta Pic and other stars using an instrument called a spectrograph," Leiden University astronomer and co-author Matthew Kenworthy said in an interview with Science Alert. "But this light curve is very strong proof because it has the shape that was predicted by another astronomer 20 years ago. The light curve we see matches the computer model he made very well."
Hiding in plain light
In order to detect faint objects (such as exoplanets and exocomets) around bright stars, many planet-hunting telescopes like Kepler and TESS rely on the
transit method of detection. Basically, astronomers plot how the brightness of a star changes over time, creating what's called a light curve. If they see a dip in the star's light curve, they analyze how long and deep the dip is, which provides them with information about what's causing the star's temporary drop in brightness.
When searching for exoplanets, astronomers look for symmetrically shaped dips that repeat over time. These indicate a symmetrical body, such as a spherical exoplanet, is orbiting in front of the star. Then, by analyzing the characteristics of the dips, researchers can tease out some of the exoplanet's properties, such as its mass and radius.
However, when searching for exocomets, astronomers don't look for symmetrical dips in the light curve. They hope to see the star's brightness drop quickly at first, then take its time returning to a baseline level. This is because comets are not perfectly round. Instead, they leave an extended tail of dusty debris behind them. Like the cometary body itself, these tails also block light, so they leave an imprint on the light curve too. And since comet tails thin out the farther you get from the comet itself, less and less light is blocked over time. In other words, the light-curve signature of a comet has a dramatic initial dip, followed by a tapered return to normal.
