Anybody out there? In two weeks, NASA will launch the Transiting Exoplanet Survey Satellite to find planets similar to ours

Arkansas Democrat-Gazette Satellite Illustration
Arkansas Democrat-Gazette Satellite Illustration

KENNEDY SPACE CENTER, Fla. -- The search for cosmic real estate is about to begin anew.

No earlier than 6:32 p.m. April 16, in NASA's fractured parlance, a little spacecraft known as the Transiting Exoplanet Survey Satellite, or TESS, bristling with cameras and ambition, will ascend on a SpaceX Falcon 9 rocket in a blaze of smoke and fire and take up a lengthy residence between the moon and the Earth.

There it will spend the next two years, at least, scanning the sky for alien worlds.

TESS is the latest effort to try to answer questions that have intrigued humans for millenniums and dominated astronomy for the last three decades: Are we alone? Are there other Earths? Evidence of even a single microbe anywhere else in the galaxy would rock science.

Not so long ago, astronomers didn't know if there were planets outside our solar system or, if there were, whether they could ever be found. But starting with the 1995 discovery of a planet circling the sunlike star 51 Pegasi, there has been a revolution.

NASA's Kepler spacecraft, launched in 2009, discovered some 4,000 possible planets in one small patch of the Milky Way near the constellation Cygnus. Kepler went on to survey other star fields only briefly after its pointing system broke. After nine years in space, it's running out of fuel.

Thanks to efforts such as Kepler's, astronomers now think there are billions of potentially habitable planets in our galaxy, which means the nearest one could be as close as 10 to 15 light-years from here.

And so the torch is passed. It will be TESS' job to find those nearby planets, the ones close enough to scrutinize with telescopes, or even for an interstellar robot to visit.

Most of the stars with possible planets Kepler spotted are far away, said Sara Seager, a planetary scientist at the Massachusetts Institute of Technology and a member of the TESS team. "TESS will fill in planets around nearby stars."

George Ricker, an MIT researcher and the leader of the TESS team, expects to find some 500 Earth-size planets within 300 light-years of here, close enough for a coming generation of telescopes on the ground and in space to examine for habitability.

The focus is on exoplanets -- planets in orbit around stars other than our sun -- but there will be more to observe.

"TESS is going to be a lot of fun," Ricker said. "There are 20 million stars we can look at."

The spacecraft will be able to do precise brightness measurements of every glint in the heavens, he said. "Galaxies, stars, active galactic nuclei," his voice trailing off.

Most of the exoplanets will be orbiting stars called red dwarfs, much smaller and cooler than the sun. They make up the vast majority of stars in our neighborhood (and in the universe) and presumably lay claim to most of the planets.

As with Kepler, TESS will hunt those planets by monitoring the light from stars and detecting slight dimming, momentary fading indicating that a planet has passed in front of its star.

IN THE SHOP

Recently TESS, partly clad in shiny aluminum foil, stubby solar panels folded modestly against its side, was sitting on a round pedestal inside a plastic tent. The tent occupied one corner of a cavernous "clean room" in a remote building on the scrubby outskirts of the space center here, amid palms and canals and flocks of cormorants.

The spacecraft is about the size of a bulky, oddly shaped refrigerator, festooned not with magnets but with mysterious nozzles and connectors. Four pairs of blue-clad legs were sticking out from underneath the pedestal, as if high-tech mechanics were working under a car.

The engineers were taping plaques to the bottom of the spacecraft, including a memory chip containing drawings by schoolchildren who had been asked to imagine what exoplanets might look like.

Standing to the side, in a "bunny suit" of protective material that left only his bespectacled eyes visible, Ricker was staring into the tent at his new spacecraft, as if he were watching his car get fixed, and exchanging rocket talk with the engineers who had designed and built it.

Ricker has been a rocket scientist, building astronomical satellites to be shot into space, for pretty much his entire career as a researcher at MIT's Kavli Institute for Astrophysics and Space Research. Most of his earlier projects involved measuring X-rays or gamma rays from snaps, crackles and pops in the cosmos, most recently the High Energy Transient Explorer, used to study the cataclysms known as gamma-ray bursts.

Asked if planets represented a departure for him, Ricker shrugged, "Not so much."

THE VAST UNKNOWN

The mission's planners say they eventually expect to catalog 20,000 new exoplanet candidates of all shapes and sizes. Particularly, they have promised to come up with the masses and orbits of 50 new planets that are less than four times the size of Earth.

Most of the known planets in the universe are in this range -- between the sizes of Earth and Neptune. Are they so-called super-Earths, mostly rock with a veil of atmosphere, or mini-Neptunes with small cores buried deep inside extensive balls of gas?

Data from Kepler and astronomers suggest that the difference is mass: Fertile rocks are often less than 1 1/2 times the size of the Earth, while barren ice clouds often are bigger. Where the line really is, and how many planets fall on one side or the other, could determine how many worlds out there are balls of freezing vapor or potential gardens.

"We need to make precise mass measurements," said David Latham of the Harvard-Smithsonian Center for Astrophysics, who is in charge of organizing astronomers to follow up the TESS observations.

Latham's team has procured 80 nights of observing time a year for the next five years on a spectrograph called Harps North, which resides on an Italian telescope on the island of La Palma in the Canary Islands, a part of Spain off the coast of Africa.

HARPS -- for High Accuracy Radial velocity Planet Searcher -- can measure the mass of a planet by how much it makes its home star wobble as it goes around in an orbit.

TESS is one of NASA's smaller missions, with a budget of $200 million; by comparison, Kepler had a budget of about $650 million. This is the first time NASA has bought a ride from SpaceX, the rocket company run by Elon Musk, for one of its science missions. All eyes will be on the launchpad, given SpaceX's history of occasionally providing unhappy, if spectacular, abrupt ends to missions.

BRIEF SHADOWS

On top of the spacecraft are four small cameras, each with a 24-degree field of view, a stretch of sky about the size of the Orion constellation.

The cameras will stare at adjacent sections of sky for 27 days at a time, and then step to the next spot. In the first year, the researchers will survey the entire southern hemisphere of the sky; in the second, they will stitch together the northern sky. If the mission is extended beyond two years, they will repeat.

Ricker and his colleagues have prepared a list of 200,000 nearby stars whose brightness will be reported every two minutes in what they call the spacecraft's postage-stamp mode. Meanwhile, images of the entire 24-degree swaths of sky will be recorded every 30 minutes.

That cadence is perfect for finding and studying current favorites in the race to locate habitable exoplanets, namely those circling the red dwarf stars, or M dwarfs, in astronomical jargon. "This is the era of the M dwarf," Seager said.

Because they are so much cooler and less luminous than the sun, their so-called Goldilocks zones -- where in principle liquid water is possible -- lie only a few million miles out from each star, instead of the 90 million miles from which the Earth circles the sun.

At the shorter distance, a year in the life of a red dwarf planet is only 10 to 30 days. So if TESS is watching that bit of the sky for 27 days straight, it could see three dips in brightness because of transits, enough to certify the planet as a real candidate and to start investigating its reality.

But reality, as Seager noted, might not be the same as habitability, at least for the fragile likes of us. Red dwarfs are very unstable and given to violent solar flares, she said.

MID-JUNE TARGET

To start its excellent adventure, TESS will be launched into an unusually eccentric orbit that takes the satellite all the way out to the moon at its farthest point. Gravitational interaction with the moon will then keep TESS in a stable 13.7-day orbit for as long as 1,000 years, Ricker said.

The great apogee, the farthest distance from Earth, will minimize obstruction and interference from our planet. The spacecraft will radio its data back once every orbit, when it is closest to Earth, at about 67,000 miles up.

But it will take almost two months and many rocket burns to get there and begin to do science. If all goes well, that would be the middle of June.

Sometime during that process, Ricker said, the team will turn the spacecraft's cameras on the Earth for a last look at home.

ActiveStyle on 04/02/2018

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