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Planet hunters launch TESS in pursuit of deeper questions − whether we’re alone in space

A SpaceX Falcon 9 rocket transporting the TESS satellite lifts off in Cape Canaveral, Fla., on April 18, 2018.

John Raoux/The Associated Press

Sara Seager has seen rockets launch before, but nothing quite prepared her for the lift-off this week of NASA’s Transiting Exoplanet Survey Satellite, known as TESS, atop a Space X Falcon 9.

While popular culture tends to fixate on the unlikely prospect that one day we’ll pick up a radio signal bearing some form of alien greeting, TESS represents a more plausible but also more ambiguous path toward answering the ultimate question of whether we’re alone in the universe.

“This one was special,” said Dr. Seager, a Canadian astrophysicist and Massachusetts Institute of Technology professor who is a long-time member of the mission’s science team. With family and friends on hand for the launch, Dr. Seager described a momentary nervousness followed by elation as the rocket ascended perfectly into the clear blue Florida sky.

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The satellite has now begun its lengthy start-up sequence, “like someone waking up from a coma,” Dr. Seager said. If all goes well, in two months, TESS will begin scanning the sky for planets around about 200,000 stars in our immediate galactic neighbourhood.

Space agencies know that such projects are well supported by a curious public, but scientists have learned to be cautious about how they frame the quest.

“TESS will find planet candidates,” Dr. Seager said. “But after that, there’s a very complicated process of follow-up.”

This is not the first time a satellite has been lofted into orbit to comb the heavens for exoplanets – the term of art for worlds circling distant suns. What makes TESS different is the systematic way in which it will scan the entire sky to take stock of what’s there and what isn’t.

“It’s all about understanding diversity,” said Jason Rowe, who holds at the Canada Research Chair in exoplanet astrophysics at Bishop’s University in Sherbrooke. “We have to think well beyond the study of individual objects. We have to think about populations of objects.”

In other words, the truths that TESS yields will be significant. But, like Billy Beane’s division-clinching Oakland A’s in Moneyball, they are truths that will emerge only in the aggregate.

To achieve its two-year mission, TESS will draw on one of the oldest and most basic tasks in astronomy. As it carefully scrutinizes its target stars, it will look for minuscule dips in brightness that occur at regular intervals. They may be due to one or more planets crossing in front of a star and temporarily blocking a fraction of its light. Because closer planets orbit more quickly, the frequency with which these dips recur provides the distance of the planet from its sun and therefore its temperature. The amount that the star dims reveals the planet’s size, helping to distinguish between a gas giant like Jupiter or a comparatively tiny rock like Earth.

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Planets that are identified this way can be further explored through other means by studying the way they influence the stars they orbit. Massive planets come with powerful gravitational fields that tug at a star, first in one direction and then the other as they circle around. In this way, astronomers can distinguish between planets that are packed with metal and those that are mostly ice. Scientists hope to use data from TESS to build up a comprehensive catalogue of possible worlds, showing which kinds of planets tend to form under which circumstances, all of which is relevant to the search for life.

Of particular interest will be the number and nature of “super-Earths” and “gas dwarfs” – planets that are more massive than our own but not at the scale of the smallest giant planets, such as Neptune. Our solar system lacks such a world, but results from the Kepler mission, which was the trailblazer for TESS, suggest they may be the most common type of planet there is.

Many of the questions that scientists are most curious to answer concern the atmospheres of exoplanets. Every planet is born with a primordial envelope of gases that can evolve over billions of years and ultimately determines what the conditions on the planet’s surface are like (assuming there is a surface).

“It’s especially important once you start asking questions about habitability,” said Dr. Rowe.

In our solar system, a smothering and toxic atmosphere has rendered Venus unlivable while Earth’s thinner atmosphere allows for liquid water and life, even though the two planets are essentially identical in size and composition.

Once TESS starts finding planets, the most significant follow-ups will be those that manage to detect and measure the atmospheres of the newfound worlds to see what they are made of. This can be done by studying how starlight is filtered through the atmosphere because different gases absorb different colours of light. The James Webb Space Telescope, a NASA project in which Canada has partnered, is set to play a key role in the story once it launches in May, 2020.

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But TESS will surely find more planets than an all-purpose telescope with competing priorities can hope to study. With this in mind, the European Space Agency has just given the green light to ARIEL, a satellite that will be built specifically to study exoplanet atmospheres.

The best-case scenario would be to measure an atmosphere in which a particular constituent cannot be explained by non-biological processes. On Earth, this is true for oxygen, which is constantly replenished by living plants. But, it’s just as likely that ARIEL will find something less definitive and potentially more intriguing.

“I think we will need to be extremely careful to not overinterpret things,” said Giovanna Tinetti, a physicist at University College London and principal investigator for the mission. “Before we can say for sure what [a] habitable planet looks like it would be good to understand what an uninhabitable planet looks like.”

The significance of TESS is that it opens the door for scientists to do just that.

“We’ve crossed the threshold in terms of capability,” Dr. Seager said. “Now Nature just needs to co-operate.”

TESS – NASA’s new planet hunter

Transiting Exoplanet* Survey Satellite (TESS)

Thermal blankets

Solar arrays

Sun shade

Finding

planets:

TESS

detects

tiny changes

in the brightness

caused by the transit

of planets across

the face of stars

Field of view

TESS

surveys

the sky in

26 sectors

Four

cameras:

Can observe

about 1/18th

of the entire

sky at any

one time

Planet

Brightness

Star

Light

Time

*Planets orbiting stars outside our solar system

graphic news, Sources: NASA; SpaceX

TESS – NASA’s new planet hunter

Transiting Exoplanet* Survey Satellite (TESS)

Thermal blankets

Solar arrays

Sun shade

Finding

planets:

TESS

detects

tiny changes

in the brightness

caused by the transit

of planets across

the face of stars

Field of view

TESS

surveys

the sky in

26 sectors

Four

cameras:

Can observe

about 1/18th

of the entire

sky at any

one time

Planet

Brightness

Star

Light

*Planets orbiting stars outside our solar system

Time

graphic news, Sources: NASA; SpaceX

TESS – NASA’s new planet hunter

Transiting Exoplanet* Survey Satellite (TESS)

Fairing:

World’s

largest.

Can carry

a payload

the size of

a school bus

Thermal blankets

Solar arrays

Sun shade

Finding

planets:

TESS

detects

tiny changes

in the brightness

caused by the transit

of planets across

the face of stars

Grid

fins:

Fold up

to stabilize

first stage

on descent

for reuse

70m

Field of view

SpaceX

Falcon 9

TESS

surveys

the sky in

26 sectors

Four

cameras:

Can observe

about 1/18th

of the entire

sky at any

one time

Planet

Landing

legs:

Fold

down

during

descent

Star

Brightness

Light

Time

*Planets orbiting stars outside our solar system

graphic news, Sources: NASA; SpaceX

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