Friday, September 9, 2016

Hello? Earth Calling . . . PART 6

For Hello? Earth Calling . . . PART 1 CLICK HERE
For Hello? Earth Calling . . . PART 2 CLICK HERE
For Hello? Earth Calling . . . PART 3 CLICK HERE
For Hello? Earth Calling . . . PART 4 CLICK HERE
For Hello? Earth Calling . . . PART 5 CLICK HERE 

(This is the final post in this series.)

What's Next in Exoplanet Hunting?

We might never be able to set foot on an exoplanet ourselves but don't let that get you down. While sci-fi fantasy is always tantalizing, our scientific reality is evolving so fast that I think we can soon reach the real answer to our most basic question, "Are we alone?" We might soon be able to "see" an exoplanet directly, and learn much about it. NASA's James Webb Telescope (see below) is set to launch in 2018.

Illustration of the James Webb Space Telescope, as of 2009. Launch date is expected to be 2018. Credit NASA
Its main mission is to study the formation of distant stars and galaxies but it is also designed to directly observe exoplanets and study their atmospheres for biosignatures of life. It will be super-stable with optical components that distort the image less than a nanometer, about the size of a few atoms. It will be equipped with a honeycomb-like multi-piece mirror that is about four times larger than Hubble's mirror (Hubble Telescope is shown below).

Hubble Space Telescope departing from the space shuttle Atlantis in 1990. It is still in operation. Credit NASA
James Webb telescope will observe in near-infrared and no doubt it will deliver good exoplanet data. But its development began in 2002, and since then exoplanet astronomy has literally exploded. New technologies specific to viewing exoplanets is what we will need very soon. The history of exoplanet exploration, though short, is interesting. It started out with much speculation and many false discoveries. The first exoplanet (gamma Cephei b) was detected in 1988 by Canadian astronomers Bruce Campbell, G.A.H Walker and Stephenson Yang at the University of Victoria. This planet, a huge gas giant 1.6 times larger than Jupiter, was at the limit of detection then so the discoverers and other astronomers remained skeptical of it for years (solid confirmation of it didn't come until 2002). Some astronomers consider this team to be the true pioneers of exoplanet exploration but if you look you will notice that it is downplayed even on Wikipedia (and fair enough - they did retract their discovery). The story of their discovery, well told in this Globe and Mail article, is an interesting one full of self-doubt and heartbreak. I think it is evidence that we Canadians need to toot our own horn a bit more.

After that other confirmations of exoplanets trickled in. As astronomers began to turn their attention to exoplanets, indirect detection methods improved, and the floodgates opened. Now garnering much interest from many scientific fields and excitement from everyone around the world, scientists and engineers are already at work on ambitious next-generation space telescopes such as (NASA's) HabEx. These telescopes will be devoted to direct exoplanet imaging. They aim to achieve an optical stability in the picometer range, less than the diameter of an atom. They also plan to use even larger mirrors and observe across the visual, near-infrared and ultraviolet spectra, which will offer even more detailed exoplanet surface/atmospheric data. It might take up to 30 years before one of these telescopes is a reality, however. A mission needs to be finalized and the technology required has to be developed first.

HabEx (Habitable Exoplanet Imaging Mission) would allow us to directly observe exoplanets within about a 30 light-year radius from Earth. Another NASA mission just initiated and in concept stage is the Large Ultraviolet/Optical/Infrared(Luvoir) Surveyor, which is an even more ambitious telescope with a larger mirror. Either mission will provide groundbreaking new data by directly imaging exoplanets with incredible precision across different spectra for the first time. Direct imaging, through the James Webb telescope coming soon, and then hopefully to be followed up with one of these next-generation telescopes, is the only way to really know if a planet is potentially habitable. The light absorbed by its atmosphere must be thoroughly analyzed to know what it is composed of, what the climate and weather are like, whether the surface is protected from radiation and temperature extremes, and whether liquid water is likely to be present. Besides determining whether a planet is potentially habitable, these missions have the ultimate goal of discovering chemical evidence for extraterrestrial life.

Still in conceptual stage, HabEx will be a large space telescope that will focus first on planets that are the right distance from their stars to have liquid surface water. I suspect Proxima b will be at the top of the list. The ability to directly image this tiny faint distant planet in superb detail will be amazing.

Even with this most advanced technology, astronomers won't be able to see a round defined planet image. Instead they will see an image that is less than one pixel. That might not sound impressive but the information in that pixel is astounding. That tiny dot can be analyzed as an absorption spectrum across various wavelengths in the visible, near-infrared and UV spectra. This EM radiation is starlight that passes through the exoplanet's atmosphere twice. It is absorbed by the atmosphere and then reflected from the planet back out into space and to the telescope. The absorption bands in the spectra will tell the astronomers which elements are present in the exoplanet's atmosphere and possibly on its surface as well. Those signatures will give clues to the planet's surface temperature and pressure, overall habitability, and even signs of life that might be present if atmospheric oxygen, ozone or methane is found.

The real challenge for this technology will not be trying to capture the planet's faint image. The Hubble Space Telescope can capture images even fainter. The problem is that planets are always right next to very bright stars. As astronomer Scott Gaudi explains, there is a common analogy used to explain how much brighter stars are than their planets: its like trying to see a firefly against a searchlight, except the firefly is a thousand times fainter. The James Webb telescope will be outfitted with coronagraphs attached to it. The coronagraph is an established technology that has been used since the 1930's to block out the Sun's central disk so that we can view its coronasphere. A coronagraph works but not perfectly. HAbEx will go one step further by using two technologies. It will have a star shade as well, which is unfurled in front of the telescope and which must be perfectly matched to the star and the telescope. Watch this NASA/JPL video of how this giant sun-flower shaped shade will unfurl in space.

This star shade will be a new technology. Coronagraphs will be used while the telescope scans for suitable planets and the star shade could be unfurled for much better starlight blockage and more in-depth imaging once a candidate is found. HabEx (or the Luvoir Surveyor) could be online within a few decades. When it is, we will have not just a growing list of established exoplanets to mull over but we will obtain unique descriptions of them as well, something to really pique our imaginations! It will be very interesting to be able to directly image Proxima b, for example, and see what kind of atmosphere, if any, this rocky planet has. The question of whether it has liquid surface water might be answered as well. Meanwhile, there is a tantalizing chance that we might not have to wait decades to know this answer. Astronomers speculate that there is a 1.5 % chance that Proxima b transits in front of its star from Earth's perspective. If it does, we might have more information about it even sooner. Astronomers might be able to discern some data about its atmosphere by comparing chemical analysis of the absorption spectrum of Proxima Centauri during transit and when the planet is away from the star.

If and when HabEx, or a similar telescope, offers promising data that doesn't rule out carbon-based life on Proxima b or another nearby Earth-like planet, I suspect projects like StarChip will follow, sending a probe there to investigate further. All of this is still decades away but it is tantalizingly feasible, and we should then have our best chance yet to find solid evidence for extraterrestrial life in our universe.

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