Astrobiology

The search for life beyond Earth: habitability, biosignatures, and open questions

What is astrobiology?

Astrobiology studies the conditions required for life, where life might be able to exist beyond Earth, and how to search for it. As of today, Earth remains the only place life has ever been confirmed to exist — astrobiology is the scientific study of the question, not a claim that life elsewhere has been found.

What life as we know it requires

Every form of life we've ever studied shares certain basic requirements: liquid water as a solvent for chemical reactions, carbon-based chemistry (covered in the Organic Chemistry article) capable of building complex molecules, and a usable source of energy. This is why the search for potentially habitable environments elsewhere generally starts by looking for places where liquid water could exist.

Life in extreme places on Earth

Scientists have found living organisms, called extremophiles, thriving in conditions once thought far too harsh for any life: near-boiling deep-sea vents, highly acidic pools, deep underground rock, and Antarctic ice. These discoveries have significantly expanded the range of conditions considered potentially habitable elsewhere in the universe, since they show life on Earth is considerably more adaptable than once assumed.

How the search is conducted

Searching for life beyond Earth takes several forms: sending robotic missions to directly study other planets and moons in our solar system for signs of past or present life, and using telescopes to study the atmospheres of planets orbiting distant stars for possible chemical signs of biological activity, called biosignatures. No confirmed evidence of life beyond Earth has been found by any of these methods so far.

Why astrobiology matters

Astrobiology brings together biology, chemistry, geology, and astronomy to address one of the biggest open questions in science: whether life exists anywhere else in the universe. It has also directly driven the development of technology used to search for signs of past life on Mars and to study potentially habitable moons in our own solar system.