NASA’s TESS spacecraft will spend two years searching the sky for nearby alien worlds.
Our Milky Way galaxy is strewn with billions of planets, alien worlds still unseen by human eyes — at least for now. Only three decades ago we didn’t know if there were planets beyond our own solar system. In 1995, astronomers discovered that a star in the constellation Pegasus was wobbling back and forth, tugged by the gravity of an unseen planet, an exoplanet, a hot and hellish world unfit for life as we know it. The wobble method of planet hunting relies on sensitive spectroscopes. As an orbiting planet tugs on its star, the starlight we see shifts from blue to red and back again.
The Kepler space telescope was launched in 2009. It found thousands of exoplanets by staring at a small patch of the Milky Way. Kepler didn’t look for wobbles. It looked for small dips in starlight, when a planet crosses in front of its star. Kepler found systems of planets, groups of worlds swirling around their star, lonely planets encased in ice, other worlds scorched by fire, newborn planets shrouded in dust, waterworlds, and planets swept by global storms, planets dancing in orbit with two stars, or even three, and even planets from other galaxies that were swallowed up by the Milky Way.
In recent years, astronomers have taken the first direct images of exoplanets, blurry pixels of alien landscapes. We’ve discovered a free-floating planet not bound to any star. And we’ve seen signs of planets being born, infant worlds scoring dark rings in the dust around their stars.
Now a new planet hunter will join the search. On April 16, 2018, the Transiting Exoplanet Survey Satellite, or TESS, will lift off from Cape Canaveral. TESS will spend two years scrutinizing the entire sky, watching nearby stars for minute dips in brightness caused by a nearby alien world. TESS’ four cameras cover a swath of the sky 96 degrees tall. TESS will divide the sky into sections like the slices of an orange and stare at each section for 27 days, then move on to the next. After two years we will have covered the whole sky.
TESS will fly an unusual orbit, swooping as far out as the moon every two weeks before falling back close to Earth and dumping a torrent of data to eager astronomers. TESS is a target hunter. The planets it finds can be studied by the next generation of telescopes on Earth and in space. With luck TESS will discover worlds suitable for lakes and oceans, with rich atmospheres and chemical signals we can detect. Their gases could tell us whether these planets are habitable or inhabited by the likes of us.
The Milky Way holds more planets than stars and a diversity that we still haven’t begun to plumb. In the search for life and meaning in the cosmos, our own world is still the gold standard.