Will we discover simple life somewhere? Maybe on Enceladus or Europa in our Solar System, or further away on an exoplanet? As we get more proficient at exploring our Solar System and studying exoplanets, the prospect of finding some simple life is moving out of the creative realm of science fiction and into concrete mission planning.
As the hopeful day of discovery draws nearer, it’s a good time to ask: what might this potential life look like?
People often seem surprised when they learn that NASA doesn’t just look out to the other planets, stars, and galaxies. It’s also an agency that studies our own home planet—from space! And why not? Earth is part of the solar system, too. So, to that end, there’s a new Earth studies mission called EMIT on its way to the International Space Station. It’s designed to track dust as it moves from one place to another on our planet through through our atmosphere.
The official name of the mission is the Earth Surface Mineral Dust Source Investigation (EMIT, for short). It will use a high-tech imaging spectrometer to study dust around the globe over the next year.
The next step to understanding exoplanets is to understand their atmospheres better. Astronomers can determine a planet’s mass, density, and other physical characteristics fairly routinely. But characterizing their atmospheres is more complicated.
Astronomers have had some success studying exoplanet atmospheres, and spacecraft like the James Webb Space Telescope and the ESA’s ARIEL mission will help a lot. But there are thousands of confirmed exoplanets with many more to come, and the Webb has many demands on its time.
Can smaller, ground-based telescopes play a role in understanding exoplanet atmospheres?
Mars is a parched planet ruled by global dust storms. It’s also a frigid world, where night-time winter temperatures fall to -140 C (-220 F) at the poles. But it wasn’t always a dry, barren, freezing, inhospitable wasteland. It used to be a warm, wet, almost inviting place, where liquid water flowed across the surface, filling up lakes, carving channels, and leaving sediment deltas.
But then it lost its magnetic field, and without the protection it provided, the Sun stripped away the planet’s atmosphere. Without its atmosphere, the water went next. Now Mars is the Mars we’ve always known: A place that only robotic rovers find hospitable.
How exactly did it lose its magnetic shield? Scientists have puzzled over that for a long time.
WASP-76b is an ultra-hot Jupiter about 640 light-years away from Earth in the constellation Pisces. A few years ago it gained notoriety for being so hot that iron falls as rain. It’s tidally locked to its star, and the planet’s star-facing hemisphere can reach temperatures as high as 2400 Celsius, well above iron’s 1538 C melting point.
Scientists have been studying the planet since its discovery in 2013, and new evidence suggests that it’s even hotter than thought. But, almost disappointingly, there might be no iron rain after all.
In the past two and a half decades, astronomers have confirmed the existence of thousands of exoplanets. In recent years, thanks to improvements in instrumentation and methodology, the process has slowly been shifting from the process of discovery to that of characterization. In particular, astronomers are hoping to obtain spectra from exoplanet atmospheres that would indicate their chemical composition.
This is no easy task since direct imaging is very difficult, and the only other method is to conduct observations during transits. However, astronomers of the CARMENES consortium recently reported the discovery of a hot rocky super-Earth orbiting the nearby red dwarf star. While being extremely hot, this planet has retained part of its original atmosphere, which makes it uniquely suited for observations using next-generation telescopes.
Upcoming telescopes will give us more power to search for biosignatures on all the exoplanets we’ve found. Much of the biosignature conversation is centred on biogenic chemistry, such as atmospheric gases produced by simple, single-celled creatures. But what if we want to search for technological civilizations that might be out there? Could we find them by searching for their air pollution?
If a distant civilization was giving our planet a cursory glance in its own survey of alien worlds and technosignatures, they couldn’t help but notice our air pollution.
Can you picture Jupiter without any observable clouds or haze? It isn’t easy since Jupiter’s latitudinal cloud bands and its Great Red Spot are iconic visual features in our Solar System. Those features are caused by upswelling and descending gas, mostly ammonia. After Saturn’s rings, Jupiter’s cloud forms are probably the most recognizable feature in the Solar System.
Now astronomers with the Center for Astrophysics | Harvard & Smithsonian (CfA) have found a planet similar in mass to Jupiter, but with a cloud-free atmosphere.
Red dwarf stars are the most common kind of star in our neighbourhood, and probably in the Milky Way. Because of that, many of the Earth-like and potentially life-supporting exoplanets we’ve detected are in orbit around red dwarfs. The problem is that red dwarfs can exhibit intense flaring behaviour, much more energetic than our relatively placid Sun.
So what does that mean for the potential of those exoplanets to actually support life?
The ultra-powerful James Webb Space Telescope will launch soon. Once it’s deployed, and in position at the Earth-Sun Lagrange Point 2, it’ll begin work. One of its jobs is to examine the atmospheres of exoplanets and look for biosignatures. It should be simple, right? Just scan the atmosphere until you find oxygen, then close your laptop and head to the pub: Fanfare, confetti, Nobel prize.
Of course, Universe Today readers know it’s more complicated than that. Much more complicated.
In fact, the presence of oxygen is not necessarily reliable. It’s methane that can send a stronger signal indicating the presence of life.