The search for another Earth
THERE are many science fiction novels, TV shows and movies about mankind’s search for other planets that could be habitable. The search for other Earth-like planets is something that clearly resonates among us.
The reason could be our survival instinct. One day, our earth might not be habitable anymore or it might be overcrowded and we might have to colonise space in order to survive. But it could also be just a natural curiosity about life beyond planet Earth. Could there be other life forms out there?
We are still far from having the necessary technology to travel to distant planets like they do in Star Trek but NASA’s new Transiting Exoplanet Survey Satellite (TESS) will go a long way in helping us narrow down the search for other potentially habitable planets.
There are countless stars out there, so there is a necessity to narrow down the search. And space scientists have done just that. Out of the 400,000 bright stars observable by TESS, scientists have picked out 200,000 which are most likely to host exoplanets similar to Earth. Researchers from three universities: Cornell University, Lehigh University and Vanderbilt University (all in the USA) have narrowed that list further down to 1822 stars.
The new catalogue of 1822 stars was presented last month in the journal,
The Astrophysical Journal Letters, in a paper entitled: TESS Habitable Zone Star Catalog.
Lead author Lisa Kaltenegger said: “Life could exist on all sorts of worlds, but the kind we know can support life is our own, so it makes sense to first look for Earth-like planets. This catalogue is important for TESS because anyone working with the data wants to know around which stars we can find the closest Earth-analogues.”
She noted there is no telling just how many planets NASA’s TESS will actually come across in the coming years but was positive about the outlook, saying the odds were stacked “in our favour”. She added: “Some studies indicate that there are many rocky planets in the habitable zone of cool stars, like the ones in our catalogue. We’re excited to see what world’s we’ll find.” The new catalogue takes into account a few factors that play a role in locating Earthsize planets such as how long the planet takes to orbit its host star, how likely we are to observe it crossing the face of its host star twice, how much radiation the planet receives, and the size of its host star.
Generally, TESS will look at cool dwarf stars burning between 2427°C and 4727°C degrees, which are roughly half as hot as our own Sun and are approximately four light years away from Earth.
TESS will observe each of these stars for tiny drops in brightness caused by planets passing in front of them. Currently this is the best way to detect planets.
Figuring out the distance between a planet and its star requires detecting two transits across the star. The 1822 stars in the new catalogue are ones from which TESS could detect two planetary transits during its mission. Those orbital periods place them squarely in the habitable zone of their star.
The habitable zone is the area around a star at which water can be liquid on a planet’s surface, which is ideal for sustaining life. “Some studies indicate that there are many rocky planets in the habitable zone of cool stars, like the ones in our catalogue,” Kaltnegger said. “We’re excited to see what worlds we’ll find.”
Eventually, the team hopes to use the James Webb Space Telescope, slated to launch two years from now in 2021, to examine exoplanets for chemical clues that show what their atmospheres are made of and whether they are ideal for life.
Of course figuring out whether life actually exists on Earth-like planets is a different kettle of fish. It may actually require sending a probe there to examine the planets’ surfaces. That’s a different challenge on a completely different scale.
Whether there are other potentially habitable planets out there and whether life already exists in such planets are things that have intrigued us for generations. It will be a long time before we can get some definitive answers but TESS is a great leap forward in our quest to find such planets.