Lecture 30: Life on Exoplanets

Question 1

explain how atmospheric chemistry is complex and many gases have nothing to do with biology

Answer 1

volcanic gases, lighting, and atmospheric photochemistry all interact

Question 2

explain how some gases can be used as biosignature gases such as oxygen

Answer 2

oxygen highly reactive, so without constant production, it would quickly combine with other elements and disappear

so, detecting large amounts of oxygen in an exoplanets atmosphere could suggest ongoing biological activity

Question 3

why do we have to be careful of ‘false-positive’ detection of biosignature gases

Answer 3

abiotic production of oxygen by photolysis of water

the O2 so produced tends to react with rocks and become consumed

but, higher concentrations can be produced if there is lots of water or geological activity is not so great so that oxygen builds up

Question 4

when might it be hard to see a biosignature?

Answer 4

clouds etc

presence of gaseous biosignature
- gaseous biosignature can be seen (oxygen), but no surface signature exists

Question 5

why was it once hard to tell if there was life on earth?

Answer 5

because oxygen biosignatures have only existed for about 2.4 million years

Question 6

what have some people considered looking for when in search of extraterrestrial intelligence?

Answer 6

technosignatures

signs or evidence of technological activity by intelligent extraterrestrial civilisation

Question 7

what are the required characteristics of a biosignature?

Answer 7

• produced by life
• produced in negligible amounts by abiotic processes
• clearly detectable signature