UCL in the News: Searching for life on other worlds

Giovanna Tinetti is an expert on detecting signs of life across interstellar space.

She has worked at JPL, Caltech and the Institut d'Astrophysique de Paris, and has just won an Aurora Fellowship to pursue her research on biosignatures at UCL. …

Earth is the only planet that we know supports life, so what does an astrobiologist do?

A small fraction of the light that reaches us from stars that have planets is transmitted or reflected from their atmospheres. By studying the spectrum of that light we can learn a great deal about them. What I do is build detailed models of planetary atmospheres, and use them to identify the signatures of life and how we can detect them.

To do that for extrasolar planets we need first to understand in detail the atmospheres of planets in our solar system - which in a sense is our laboratory. Basically we are searching for disequilibria in the chemical state of the atmospheres of other planets. …

Can you give me an example? …

Aliens looking at the spectrum of Earth would notice the large quantities of oxygen and ozone there. Oxygen can be produced in the atmosphere of an abiotic planet, but not in the quantities that we see on Earth - and it's very reactive, so you need a constant source to keep the level at 21%. …

Oxygen is not the only biomarker. …

Photons that are good for photosynthesis are absorbed very efficiently, while the rest are scattered back as a waste product. This gives a very distinctive signature - a high reflectance in the far red of the optical spectrum. …

So is that something we can detect on exoplanets?

That's one of the questions I've been working on. You start from a 3-D model of an Earth-like planet and you play with the parameters. You look from different directions and as the planet rotates; you see how the signature changes in varying conditions of the atmosphere. …

How much of these biosignatures can we actually detect at interstellar distances?

Trying to study a terrestrial planet in the habitable zone is a real challenge. Some of the missions being planned now will enable us to do that, but unfortunately the information of an entire planet is likely to be collapsed into just one pixel.

Now you're probably thinking it's impossible to learn anything about a planet from one pixel. But not so. …

I've shown that you can still pick up biosignatures from Earth, the difference in seasons on Mars, the variation of the polar caps, the composition of the atmosphere - a whole lot of interesting information.

But can you make much progress now before terrestrial exoplanets in the habitable zone are actually detected?

We need to model for future missions, and at the same time to understand what is going on with present measurements. The extrasolar planets we can already probe are hot Jupiters. So I've published a few papers on those, and have projects with Spitzer and Hubble to probe the atmospheres of those planets. …

I guess as an astrobiologist you must believe we are going to find inhabited planets? …

I have no doubt now that if life can set up on a particular planet it will. I think it's much less probable that it will evolve from an elemental to a more complex sort of life. …

So life is almost certainly very common in the universe. Complex life probably is not.

So you think we live in a universe full of micro-organisms…

Exactly

…and hardly any humans.

Hardly any complex lifeforms. But I would be very surprised if we were the only ones. It is a huge universe.

Douglas Blane, www.scientificblogging.com/douglasblane