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Probing the Capability of Future Direct-imaging Missions to Spectrally Constrain the Frequency of Earth-like Planets
Ist Teil von
The Astronomical journal, 2021-03, Vol.161 (3), p.150
Ort / Verlag
Madison: IOP Publishing
Erscheinungsjahr
2021
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
Abstract
A critical question in astrobiology is whether exo-Earth candidates (EECs) are Earth-like, in that they originate life that progressively oxygenates their atmospheres similarly to Earth. We propose answering this question statistically by searching for O
2
and O
3
on EECs with missions such as HabEx or LUVOIR. We explore the ability of these missions to constrain the fraction,
f
E
, of EECs that are Earth-like in the event of a null detection of O
2
or O
3
on all observed EECs. We use the Planetary Spectrum Generator to simulate observations of EECs with O
2
and O
3
levels based on Earth’s history. We consider four instrument designs—LUVOIR-A (15 m), LUVOIR-B (8 m), HabEx with a starshade (4 m, “HabEx/SS”), and HabEx without a starshade (4 m, “HabEx/no-SS”)—as well as three estimates of the occurrence rate of EECs (
η
earth
): 24%, 5%, and 0.5%. In the case of a null detection, we find that for
η
earth
= 24%, LUVOIR-A, LUVOIR-B, and HabEx/SS would constrain
f
E
to ≤0.094, ≤0.18, and ≤0.56, respectively. This also indicates that if
f
E
is greater than these upper limits, we are likely to detect O
3
on at least one EEC. Conversely, we find that HabEx/no-SS cannot constrain
f
E
, due to the lack of a coronagraph ultraviolet channel. For
η
earth
= 5%, only LUVOIR-A and LUVOIR-B would be able to constrain
f
E
, to ≤0.45 and ≤0.85, respectively. For
η
earth
= 0.5%, none of the missions would allow us to constrain
f
E
, due to the low number of detectable EECs. We conclude that the ability to constrain
f
E
is more robust to uncertainties in
η
earth
for missions with larger aperture mirrors. However, all missions are susceptible to an inconclusive null detection if
η
earth
is sufficiently low.