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IN THE past 100 years, astrophysicists have deduced that space-time is expanding, that this expansion is accelerating, that the universe is about 14 billion years old and that there are at least 4000 planets beyond those in our solar system, called exoplanets. When I wrote my junior undergraduate thesis on exoplanet atmospheres back in 2002, all we knew was that simulations suggested we should see sodium in the atmospheres 鈥� and we did, but we saw less of it than expected. Today, our simulations are more sophisticated and we have moved beyond basic details about atmospheres to thinking through how to learn more about exoplanet surfaces.

Increasingly, our research on stars has become entangled with research on exoplanets too. In particular, we have become very interested in a type of star known as a red dwarf or M dwarf. These are pretty fun because they are the coolest, smallest stars that exist on the main sequence, which comprises all of the hydrogen-burning stars (as opposed to neutron stars and white dwarfs, which are just compact collections of particles). M dwarfs are totally different from our own sun, with surface temperatures that are often about half that of our star. They also tend to be less than half the mass of the sun, and the smallest ones have masses and radii that are less than 10 per cent of the sun鈥檚.

Importantly, simulations show that Earth-sized planets with extensive oceans could be abundant around M dwarfs. For this reason, they have become subjects of intense interest, but observing them isn鈥檛 simple. They are also known as red dwarfs for a reason: unlike the sun, M dwarfs aren鈥檛 bright in the visible parts of the spectrum.

To get a really good look at them, we must use infrared, the part of the light spectrum on the red side that is just beyond the capacity of the human eye to see. Anyone who has seen action heroes in films use night-vision goggles is familiar with it. Effectively, to study M dwarfs, we must use telescopes that are fitted with technology similar to that of these goggles.

鈥淭o study M dwarfs, we must use telescopes with technology similar to night-vision goggles鈥�

In many ways, astronomy is a 鈥渨ait and see鈥� science 鈥� but thanks to advances in physics and centuries of information gathering, we have become extremely good at doing that in an intelligent way. Now, we specifically design instruments that do targeted scans of the sky, surveying with specific objects in mind.

Part of our smart searching involves building specific instruments designed to capture information about the kinds of objects we want to see. The Kepler space telescope spent nine years surveying the sky, and the information it collected was photometric in nature, meaning that it measured the brightness of the stars in different parts of the light spectrum. Scientists then searched these measurements for signs of periodic dimming 鈥� evidence of a planet eclipsing the star. More than 2000 confirmed planets were discovered this way.

Today, Kepler is retired, but the search from space goes on with NASA鈥檚 Transiting Exoplanet Survey Telescope and the European Space Agency鈥檚 Gaia observatory. The information collected by these instruments is made all the more interesting by simulation work that is under way. For example, last year Aomawa Shields and Regina Carns published a paper that looked at the presence of sodium chloride dihydrate (hydrohalite) on the surfaces of M dwarf-orbiting exoplanets.

Hydrohalite can condense into sea ice at low temperatures. Unlike salt-free ice, this ice can be highly reflective in the infrared spectrum, which is exactly where we are already looking for M dwarfs. This presents the challenge of telling the difference between light coming directly from the star and starlight being reflected from the planet鈥檚 surface, but it also gives us an opportunity. Shields and Carns found that this reflectivity also enhanced the build-up of carbon dioxide, which is a key ingredient for planet habitability.

Of course, it is unclear what it means for humanity to find habitable planets. As I mentioned in a previous column, the possibility of long-distance travel to other stars during a single human lifetime is low. At the same time, as we refine data collection mechanisms, we strengthen our ability to stumble across indicators of life in far-flung places. Perhaps, more than knowing how old space-time is, this is the kind of information that could revolutionise humanity鈥檚 relationship with the universe.