TESS leaves our planet to hunt for many others

NASA’s TESS spacecraft launched successfully on Thursday (Australian time) from Cape Canaveral, Florida, kick-starting a new era of exoplanet discovery that will focus on finding planets in our own stellar neighbourhood.

The Transiting Exoplanet Survey Satellite, or TESS for short, hitched a ride on a SpaceX Falcon 9 rocket. It was slated for launch on Monday April 16, but was delayed for two days due to an issue with the rocket — but eventually it lifted off without a hitch. By June it will settle into a unique, looping orbit that soars out to 250,000 kilometres from Earth before swooping back in to within 100,000 kilometres.

TESS is designed to hunt for alien planets around 200,000 of the nearest and brightest stars in our galaxy. When a planet’s orbit swings in front of its star, it blocks out a tiny portion of the star’s light. TESS will aim to detect this tell-tale drop, potentially discovering thousands of new worlds, from Earth-sized rocky planets to colossal gas giants.

“TESS will really tell us what about the population of planets in our local solar neighbourhood and especially around red dwarfs,” says Brad Tucker, an astrophysicist from the Australian National University. 

Unlike previous surveys, which either found all kinds of planets around distant stars or large planets around nearby ones, TESS will be able to discover small planets around bright nearby stars. 

One of the mission’s biggest goals is to find out how common it is for a terrestrial planet to orbit in the habitable zone — the sweet spot around a star where the temperature is just right for liquid water to exist. 

According to Natalia Guerrero, a researcher in the TESS Science Office at the MIT Kavli Institute for Astrophysics and Space Research in Massachusetts, US, this means “we will be able to better understand where our solar systems fits within the wider picture of planetary formation and better understand whether we are common or unique.”

TESS’s predecessor, NASA’s Kepler Space Telescope, was similarly designed to find Earth-sized exoplanets in the habitable zone. Over the past decade it has been a powerhouse of discovery, finding over 2000 confirmed new planets, including many that could potentially harbour life. 

But Kepler’s job was to stare at 150,000 distant stars in a small region of the Milky Way, while TESS will look much closer to home. It will focus on stars within a few hundred light years that are 30 to 100 times brighter than those Kepler observed.{%recommended 6187%}

“Kepler was a ‘statistical mission’,” explains Guerrero, “meaning it carefully measured everything within a specific patch of sky it observed and completed a ‘census’ of the stars in that field of view.

“TESS is doing a survey of stars which can be easily followed up by ground-based and space telescopes, sweeping across 85% of the sky in just two years.” 

The satellite will measure a planet’s size and orbit, and then follow-up efforts will measure mass, allowing astronomers to better understand its composition. Powerful telescopes such as Hubble and NASA’s upcoming James Webb Space Telescope, due to launch in 2020, will also study the planetary atmospheres in detail.

But if TESS discovers as many exoplanets as anticipated, observing time might be stretched.

“This is really going to be a case of ‘too many planets, not enough telescopes’,” says Jonti Horner, an astronomer at the University of Southern Queensland (USQ), Australia.

Facilities are currently being built to analyse TESS’s discoveries, and Australia will be playing a key role. USQ’s Mount Kent Observatory on Queensland’s Darling Downs will host the only dedicated follow-up facility in the southern hemisphere: MINERVA-Australis. Together with its northern-hemisphere counterpart in Arizona, US, the observatory will scour the skies for new worlds.

“A cool part, from the Australian perspective, is that the first year of TESS’s mission will be spent looking at stars in the southern sky,” says Horner. “So we’ll be getting a stream of potential planets from TESS to follow up — and our role will be to confirm that those planets really exist, as well as doing all we can to learn more about them.”

But exoplanets aren’t the only intriguing objects that TESS has set its sights on. Since it will excel at measuring very quick changes in light, it will also be equipped to study supernovae and other brief, explosive events. This will help astronomers study the evolution of these explosions in incredible detail.

“By monitoring such a large patch of sky when compared to Kepler, we’ll see more galaxies … and therefore even more supernova!” Tucker says. 

A new instrument has also just come online at the Siding Spring Observatory in NSW, which will soon launch the FunnelWeb survey.

“This will measure the properties of the stars that TESS is looking at to help put a complete picture together of the new stellar systems that are discovered,” Tucker says.