A brief history of zombie stars, habitable zones, and the search for alien life


The Transiting Exoplanet Survey Satellite launches in 2017.

In recent years, astrophysicists and space researchers have made a series of startling announcements.

Zombie star systems, Earth-size planets, and habitable zone candidates.

On Thursday, a team from the Max Planck Institute for Astronomy announced they had discovered an atmosphere around a small Earth-like planet - a first for space research.

An artist's impression of an exoplanet with a detectable atmosphere.

An artist's impression of an exoplanet with a detectable atmosphere.

In 2016, an atmosphere was detected around super-Earth 55 Cancri e, but this massive world is too large and weird (a year lasts less than 18 hours) to be considered as "Earth-like".

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In just two decades, more than 3000 exoplanets have been detected, mainly as a result of the Kepler space mission.

How close is this to discovering life?

The researchers are "cautiously optimistic" the atmospheric planet - GJ 1132b - has an Earth-like atmosphere and it's a step forward in the search for life on other planets.

They pointed out it was not the discovery of extraterrestrial life, but, according to their calculations, the models suggest an atmosphere rich in water and methane, the building blocks of life on Earth.

Light split into constituent wavelengths can be analysed to detect the presence of gases.
Nasa Exoplanet Exploration

Light split into constituent wavelengths can be analysed to detect the presence of gases.

It's been dubbed a "super-Earth", which has a nice ring to it, and is 39 light years away in the Vela constellation, which you can see from the Southern Hemisphere. It has a radius 1.4 times that of Earth and a mass of 1.6 times our planet.

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"[The] detection of an atmosphere around the super-Earth GJ 1132b marks the first time an atmosphere has been detected around a planet with a mass and radius close to that of Earth."

Up until the announcement on Thursday, there were very few observations of light from exoplanet atmospheres and they all involved gas giants or large-mass worlds.

"With the present observation, we've taken the first tentative steps into analysing the atmosphere of smaller, lower-mass planets that are much more Earth-like in size and mass."

Of course, there are caveats.

The margin for error in interpreting data suggesting the presence of water means the entire planet's surface could be covered in water with an atmosphere of steam.

The search for exo-planets (exo meaning beyond our solar system), has accelerated since the first definitive discovery of outer space planets in 1992.

As of 2017, 3609 exoplanets have been detected in 2703 planetary systems. There's a bit of disagreement among astronomers about confirming some of those worlds as planets - as opposed to meteors or data glitches.

Nasa, for instance, recorded 3472 confirmed exoplanets.

Discovering planets is one thing; discovering a planet with an atmosphere, or even a potentially Earth-like habitable atmosphere, is the holy grail.

Astronomers are looking for "bio-signatures" by analysing light split into wavelengths, which they can use to determine the type of gases present in an atmosphere.

By searching for "transiting" planets, when worlds pass in front of a host star, the dip in brightness can be interpreted to determine, for example, planetary mass, atmospheric composition, and radii.

Nasa's exoplanet program analyses data gathered from these wobbles in brightness, splitting the constituent wavelengths of light to determine the presence of gases.

"When we analyse light shot by a star through the atmosphere of a distant planet - a technique known as spectroscopy - the effect looks like a bar code. The slices missing from the light spectrum tell us which constituents are present in the alien atmosphere."

MIT physics professor Sara Seager also tackled the problem of the unknowable constituents of alien life.

"The theory ended up being, we should maybe consider all potential molecules that could be in gas form.

"Why not consider all of them? I just combine them in any way possible, like just taking letters in the alphabet and combining them in all ways."

That initial 1992 discovery, two planets orbiting a pulsar with the catchy name PSR B1257+12, is worth revisiting because of its odd, nightmarish, characteristics.

"The entire system is a graveyard, remnants of what used to be a normal functional solar system before the star blew apart in a giant explosion known as a supernova.

"The massive shockwave from the supernova stripped away any atmosphere or living creatures that might have once lived on these planets, leaving behind ghostly, rocky shells, dead planets orbiting the corpse of an extinct star."

The collapsed star in the system is a pulsar - a "zombie" sun - spinning a full rotation every 6.2 milliseconds and emitting a beam of radiation detectable on Earth.

The first Earth-sized planet discovered in a habitable zone was Kepler-186f, a discovery that confirmed Earth-like worlds could exist in habitable zones outside our solar system.

"Many of the planets found so far are gas or ice giants, with little chance of a solid surface harbouring a warm little pond. But we've also found some rocky worlds in Earth's size-range.

"Even with the expected advances in observing technology in years to come, we're unlikely to know the precise nature of any life we might detect...Still, among those rocky, Earth-like worlds, we could catch tantalising glimpses of the right conditions for life," the Nasa Exoplanet Exploration mission statement says.

Those "just right" conditions have so far been detected on a handful of exoplanets - but the ultimate aim of the Nasa program and other astronomical research institutes is to find signs of life on other worlds.

Terrifying exoplanets have been discovered: worlds with boiling atmospheres, or covered in ice.

There was much excitement in 2015 when scientists announced they had discovered a planet in a habitable zone and it was Earth-sized.

And, earlier this year, the Spitzer telescope detected a system of seven Earth-sized planets orbiting a single star.

The Kepler space telescope is the flagship for the ongoing search for planets outside our system.

In 2017 and next year, NASA plans to launch a new satellite telescope, TESS (Transiting Exoplanet Survey Satellite), with a mission to scan another 200,000 star systems, in addition to the Kepler's 150,000 star sweep.

Citizen astronomers can also help analyse data in the search for new worlds.

 - Stuff

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