To Seek Aliens We Need to Look at Earth Through Their Eyes

Article by Elizabeth Rayne                                    April 5, 2021                                   (syfy.com)

• A research team from the Johns Hopkins Applied Physics Laboratory think that observing Earth from the perspective of distant extraterrestrial beings could help astronomers see our world through extraterrestrial eyes. And in turn, this can help our own scientists new insight on how to look for habitable – and inhabited – exoplanets.

• Researchers Noam Izenberg, Kevin Stevenson and Laura Mayorga recently presented the objective of the Earth Transit Observer (ETO) mission concept to the 52nd Lunar and Planetary Science Conference, hoping to get a green light to pursue the idea.

• Astronomers have been using the ‘transit method’ of finding and studying exoplanets since 1999. When a planet is orbiting in front of its star, the starlight will dim and brighten again when the planet has moved on. Particles in a planet’s atmosphere absorb starlight at some frequencies to indicate a planet in transit. What the ETO team wants to determine is whether more can be applied to this method in the future.

• The research team pointed out that the fundamental problem in exoplanet science is that we only know an exoplanets as well as we know their host star. Stars have varying degrees of brightness throughout. Starspots (like sunspots) can make scientists think they are seeing in a transiting planet. Sunspots on our own Sun are well documented. But starspots on distant stars remain largely unknown. Also, most exoplanets are too close to their stars to make out continents and oceans.

• “Even if you can separate the planet from the star, the Earth is reflecting and absorbing sunlight at different wavelengths,” say the researchers. “For a star to be a good reference it either needs to be unchanging, or you need a good understanding of how it changes.”

• Atmospheric particles that absorb starlight can indicate whether an exoplanet has anything close to the air we breathe, or if it rains everything from metal to lava. One exoplanet is so hot that it not only vaporizes metal, but tears the vapor molecules until the dismembered atoms are blown to its cooler night side to regroup.

• Future NASA astrophysics missions using space telescopes like TESS, Hubble and the soon-to-be launched James Webb Space Telescope will require stacking dozens of transmission spectra to build up sufficient signal for the relatively small atmospheres on exoplanets. “An Earth transit observer will test how well stacking can be done or if other strategies are needed,” say the researchers.

• What an ‘Earth transit observer’ is likely to see is a pale blue dot, watery and covered in clouds with an atmosphere of nitrogen and oxygen in which water vapor precipitates. Reflected light can give away whether a planet has oceans, while planet life has very low reflectivity. Any celestial body with water is seen as having a higher chance of being habitable. There are also traces of methane in our atmosphere that could tell an alien observer that our blue planet could be swarming with life.

• Earth may not be so easy to demystify from an alien’s perspective, however. Sun flares and coronal mass ejections of plasma can mess with how our transiting planet is seen. Then there are the constantly changing planetary seasons of Earth that can also throw off an alien astronomer’s observations. “These lessons are then directly transferable to exoplanet observations,” say researchers. Of course, there may be creatures out there that breathe poison. Even some Earth bacteria can eat rocks and metabolize methane. So you have to expect anything.

Suppose there really are aliens out there who are creeping around on the surface of

some faraway planet and have managed to survive everything space has thrown at them so far. How could we find out they exist?

The answer might lie in how they would (hypothetically) see us. We may never know whether there really are intelligent beings who have spotted our planet as it passed by the sun, but observing it from their perspective could help us see through extraterrestrial eyes. This is the objective of the Earth Transit Observer (ETO) mission concept. Led by a research team from

the Johns Hopkins Applied Physics Laboratory (APL), ETO will watch Earth in transit as if it was a spacecraft sent out here by other intelligent beings.

Researchers Noam Izenberg and Kevin Stevenson, who will be the project leads if this

mission becomes reality, and co-led a study recently presented at the 52nd Lunar and Planetary Science Conference, and Laura Mayorga, who also co-led the study, believe that observing Earth from the perspective of a being who never knew it existed could give us new insight on how to look for habitable—and possibly inhabited—planets.

“While an earth transit observer will not explicitly help us detect exoplanets, it will help us understand them and tease out their possible habitability signatures better. There is a

fundamental problem in exoplanet science in that we only know planets as well as we know their stars,” they said.

Astronomers have been using the transit method of finding exoplanets since 1999.

This method determines when a planet is orbiting in front of its star, which causes starlight to dim while it is being obscured and brighten again when the planet has moved on. Particles in a planet’s atmosphere can also absorb starlight at some frequencies, and the light that makes through can tell the observer how much was absorbed and whether that is a sign of a planet in transit. What the ETO team wants to know is whether there is more that can be applied to this method in the future.

The problem with stars is that they have varying degrees of brightness throughout, with starspots (like the sunspots in our own star) can warp what scientists think they are seeing in a transiting planet. However, the dark spots on our Sun are documented and followed, so scientists know how they change over time. Starspots on distant bodies remain largely unknown. When there is no clear idea of their size or distribution, they can mess with observations. Most exoplanets are also too close to their stars to make out the continents and oceans they may have.

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