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Artist illustration provided by NASA
TESS is to spend two years in orbit searching for alien planets.

Editor's note: A version of this was previously published on the author's website.

NASA’s new planet hunting satellite, TESS, has entered its planned orbit, says a Utah native who is a member of the science team analyzing data to discover planets beyond the solar system — and the last he checked it was "operating properly.”

The Transiting Exoplanet Survey Satellite launched from Cape Canaveral Air Force Base, Florida, on April 18. It looped through a unique program of complex orbits, taking it around the Earth three times and past the moon before settling into a stable orbit that will bring it between both bodies. TESS promises to open an era of even more dazzling discoveries of alien planets.

Jason Steffen of the Department of Physics and Astronomy at University of Nevada, Las Vegas, spoke on June 27 at Clark Planetarium about the findings of the Kepler satellite — which is nearing the end of its lifetime, as its fuel runs out — and its vastly improved successor, TESS. The free public session in the planetarium's IMAX Theater was part of a series of the planetarium's ongoing Summer Lecture Series.

Joe Bauman
Dr. Jason H. Steffen, associate professor in the Department of Physics and Astronomy, University of Nevada, Las Vegas, speaks at Clark Planetarium in Salt Lake City on June 27. He is from Fruit Heights, Davis County, Utah, and graduated from Weber State University in Ogden. He earned his master's and Ph.D. degrees in physics from the University of Washington, Seattle.

Steffen has been part of NASA's planet-finder team since 2008, the year before Kepler began its discoveries. Like Kepler, TESS will be a "catalyst" for other instruments following up on indications of alien planets, he said. Detections will come when any of TESS' four CCD cameras notice dimming of starlight, an indication of a planet passing between the star and Earth. Although nearly all stars are believed to have planets, a small fraction will happen to cut between their stars and Earth. NASA calculated that only 1 percent of solar-type stars with planets would show transits from our location.

Discovering them requires precision pointing and extremely sensitive instruments. If a TESS-type planet finder were launched by a civilization in another star system, it would detect only a 1 percent dimming of our sun when the largest planet, Jupiter, transited. Earth's dimming would be only one-tenth as much as Jupiter's, Steffen added.

With those difficulties and the low likelihood that a planet's orbit would cause it to transit, Kepler's discoveries still amounted to 4,034 planets and planet-candidates as of June, he said. Some were as tiny as the moon. In an exciting development, Kepler has found stars with multiple planets.

Speaking of the first of these star systems to be detected, three planets orbiting the star called Kepler-9, he said, "After … five long years of waiting we saw its signal in this system." A 2012 paper in which he was the lead author confirms that multiple stars host more than one planet — in this study, 27 planets in 13 star systems.

Steffen said that throughout the cosmos, "there are as many stars in the sky … as there are grains of sand on the Earth." That includes all beaches, sand dunes, deserts and other sand deposits. Even with the limitations of Kepler, many Earth-size planets have been discovered and some are in the so-called habitable zone, the orbital distance where liquid water can exist on a planet's surface.

NASA
An infographic provided by NASA shows the TESS satellite's components.

"Almost 100 planets from Kepler would be in the habitable zone," he said. The term doesn’t necessarily mean life could exist there; it means that the temperature is believed to be right — but other conditions might make a planet uninhabitable, such as a highly corrosive atmosphere or powerful flares from a nearby star.

Kepler kept track of only one small section of the sky, about 100 square degrees, “the size of the palm of your hand at arm’s length.”

Because Kepler stared at a small wedge extending far into the galaxy, its average planet is about 3,000 light-years away, he said.

TESS will be the first planet-finder to search the entire sky, 40,000 square degrees, or 400 times the Kepler region. TESS will aim at the nearest and brightest stars, many about 300 light-years away. That closeness means they can be studied more thoroughly by instruments such as Earth-based observatories, Hubble and the James Webb telescope (once it gets into orbit). Nearer than Kepler's targets, these stars will be 30 to 100 times brighter and therefore easier to examine in detail, according to NASA.

NASA adds, "TESS planets should be far easier to characterize with follow-up observations. These follow-up observations will provide refined measurements of the planet masses, sizes, densities and atmospheric properties." If an alien atmosphere has certain markers, they could indicate the presence of life.

Still, with its limitations, Kepler's discoveries are amazing. Steffen showed a chart depicting properties of the 4,034 planets and planet-candidates Kepler has found as of June. The findings about size of planets prompted astronomers to wonder why none in the solar system are between Earth-size and four times the mass of the home planet, although some exist on either side of the gap. Kepler has seen thousands between those sizes, Steffen said.

With the expected new results from TESS — maybe 3,000 planets of 300,000 star systems examined, with "a huge number" close to Earth size — "We can understand how whole planet systems are put together," he added. Astronomers expect to learn "how terrestrial planets (like Mercury, Venus, Earth and Mars) relate to each other" in other star systems, as well as the roles of gas giants like Jupiter, Saturn, Uranus and Neptune.

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Seth Jarvis, the planetarium director, remarked that TESS is "sort of Kepler on steroids." TESS is about 5 feet tall and, with solar panels extended, more than 12 feet long. Yet it will operate on 500 watts of power, Jarvis said — half that of a coffee-maker.

Asked about interesting planets, Steffen said one rocky example is so close to its star that the heat is evaporating it, leaving a comet-like tail. But he also said, "By far the most interesting planet we’ve ever discovered is the one we’re sitting on."