That mythical box Pandora should have never opened might have unleashed all sorts of terrors on Earth, but there could be much more tantalizing things hiding in the depths of space.
Millions of secrets are hiding the atmospheres of exoplanets. Now that we are transitioning from exoplanet discovery to characterization, NASA wants to launch its Pandora mission around the same time as the James Webb Space Telescope (JWST) to see what is really out there. There has been one problem plaguing past planet-hunting telescopes including Kepler, Spitzer, Hubble and even TESS. Stars have gotten in the way and made it look like some transiting exoplanets had characteristics that actually belonged to those stars.
What lurks in the atmospheres of these planets, most of which are too distant to send a spacecraft to, is the proverbial box Pandora seeks to open.
“Transits let us study the makeup of exoplanets’ atmospheres by comparing the size of an exoplanet’s shadow at different wavelengths or colors of light,” Pandora co-investigator Benjamin Rackham told SYFY WIRE. “Through this technique, known as transmission spectroscopy, we can infer the presence of different atoms or molecules in an exoplanet’s atmosphere by identifying wavelengths where the exoplanet casts a larger shadow.”
Pandora is a SmallSat with huge potential. It is equipped with an 18-inch mirror that will catch exoplanets transiting K and M-type stars. These are cool, low-mass stars that might host many potentially habitable planets, which Rackham believes could be anything from hot Jupiters to super-Earths to smaller sub-Neptunes. With the unprecedented ability to observe transits with two detectors, one that see visible light and another that sees in the near-infrared, it will be able to separate what characteristics belong to a star versus which identify a transiting exoplanet. Disruptive signals from stars will be attributed to the stars. If it identifies water vapor like that in the atmosphere of Mars, or organics like those floating around above Titan, scientists back at mission control will be certain that they are seeing the right observations.
Before we look past a planet’s atmosphere to see what lies (and could be crawling) beyond, we have to look into the atmosphere itself. By finding out more about their atmospheres, scientists can at least get an idea of what that planet is like, and whether or not it might be habitable. Water vapor in the atmosphere may or may not mean habitability. The problem is that the starspots on some cooler stars may actually be cool enough to contain water vapor. If an observing spacecraft picks those up at the same time a planet is transiting, it could beam back data that makes it appear as if water vapor exists on the planet.
“The near-infrared spectrum will let us search for water absorption features, and the optical data will clue us in to brightness changes of the star that point to starspots,” Rackham said. “Pandora is that we will be able to record long transit baselines before and after the transit to probe really well for these brightness changes.”
Meaning, Pandora will stalk stars for about 24 hours around each transit and keep stalking them up to ten times a year. This is what will provide such a long baseline of data in the visible and near-infrared spectra, which will help separate starspots from anything in the atmospheres of the exoplanets flying past them. From this data, NASA scientists on the home planet will create digital models of the host stars that include their spots so they better understand the conditions within these starspots and how they affect transit observations. Rackham is eager to see Pandora in action along with JWST.
“Pandora’s targets are all also high-priority targets for JWST. JWST will collect the best transmission spectra yet possible for these targets,” he said. “The Pandora data will help us place the JWST observations in the context of the observed stellar activity for these systems, allowing us to constrain the impact of starspots and make the most of the JWST data.”
So what could be out there beyond out solar system? If planets where it rains lava or molten iron have already been found, weirder atmospheres may exist.