It's almost a certainty that we're not alone in the universe, but so far direct evidence has eluded us. While we have some idea about what kinds of signs to look for on other planets, many of these can also be created under natural processes. Now NASA is about to launch a new mission that can help root out these false positives by studying the interactions between stars and their planets.
Since Earth is the only place we currently know for sure has life, it makes sense that astronomers would look for similar worlds out there. While signs of technology like communications are one avenue that's being explored, discovering microbial, plant or animal alien life would be just as momentous, and natural biomarkers like oxygen or methane gas in the atmosphere could give away their presence.
But the problem is, they aren't entirely reliable indicators. Gases like oxygen can get into planetary atmospheres without life under some circumstances, and just looking at the planets themselves doesn't give the whole picture – the stars they orbit play a huge part too.
For example, red dwarf stars are cooler and smaller than our Sun, and so they interact with the atmosphere of orbiting exoplanets differently. They also tend to throw off more ultraviolet light, and in simulations scientists have shown when this UV light hits the atmosphere of an exoplanet, it can strip carbon out of carbon dioxide molecules. That leaves behind molecular oxygen, which could be misinterpreted as a sign of life.
"We call these false-positive biomarkers," says Kevin France, an astronomer at NASA. "You can produce oxygen on an Earth-like planet through photochemistry alone. If we think we understand a planet's atmosphere but don't understand the star it orbits, we're probably going to get things wrong."
The new mission, led by France and his team, is designed to help identify these false-positives and stop them muddying the waters as we search for extraterrestrial life. Known as Suborbital Imaging Spectrograph for Transition region Irradiance from Nearby Exoplanet host stars (SISTINE), this mission will study targets in the far-UV light range, with wavelengths between 100 and 160 nanometers, which most existing telescopes can't measure.
Within that range, UV light can create oxygen in the atmospheres of some planets. Knowing that, astronomers can check red dwarf stars and understand that any oxygen-rich readings of planets orbiting them should be taken with a grain of salt.
SISTINE will fly onboard a Black Brant IX sounding rocket, short missions that briefly touch the edge of space before coming back down again. In all, the mission only gets about five minutes of observing time, but that should be enough to make these kinds of observations.
The first mission is due to take off today, August 5, from White Sands in New Mexico. This calibration mission will see SISTINE reaching a maximum altitude of 174 mi (280 km) to observe NGC 6826, a nebula that's strong in UV light.
Then, a follow up SISTINE mission will launch in Australia in 2020. This time, the instrument will observe the UV light coming from Alpha Centauri A and B. These missions will help back up new telescopes like James Webb, which can see in wavelengths from visible to mid-infrared.
Source: NASA