Table 3.

Possible virus detection methods: how can we detect extraterrestrial viruses?

Virus detection method	Advantages	Challenges
Infection	Highly specific for virus identification and host response	1. Requires correct host 2. Requires suitable conditions
Virion detection	Unique structures enable direct detection	1. Virions may not represent active viruses 2. Could produce false positives
Metagenome sequencing	Very broad net theoretically allowing any virus to be identified	1. Sequences may not resemble known viruses 2. Nucleic acid may be hard to purify or amplify 3. Exoviruses may not contain nucleic acids
Virus effects on hosts	May be detectable remotely	1. May be difficult to differentiate between infected and uninfected hosts 2. No detectable hosts In environment
Microscopy indicators (SEM, TEM, AFM)	Provide potential indication of viruses to be confirmed by methods above	1. Typical virion size is small 2. Very high resolution is necessary 3. Morphologies may be indistinct

Of the currently known methods for virus detection, those suitable for astrobiology applications are challenging to imagine but we can leverage off the suite of methods already in use on Earth.