The Habitable Zones of Pre-Main-Sequence Stars - Ramses Ramirez (SETITalks)
Δημοσιεύτηκε στις 6 Ιαν 2015
Ramses Ramirez
Cornell University
The
habitable zone (HZ) is the region around a star in which liquid water
could exist on a planetary surface. Although most HZ studies have
focused on the main-sequence period, here we argue that the
pre-main-sequence HZ likely provides additional targets for observers.
The spatial distribution of liquid water and its change during the
pre-main-sequence phase of protoplanetary systems is important in
understanding how planets become habitable.
Such worlds are
interesting targets for future missions because the coolest stars could
provide habitable conditions for up to 2.5 billion years post-accretion.
Moreover, for a given star type, planetary systems are more easily
resolved because of higher pre-main-sequence stellar luminosities,
resulting in larger planet-star separation for cool stars than is the
case for the traditional main-sequence (MS) habitable zone (HZ). Using
1-D radiative-convective climate and stellar evolutionary models, we
calculate pre-main-sequence HZ distances for F1-M8 stellar types. We
also show that accreting planets that are later located in the
traditional MS HZ orbiting stars cooler than a K5 (including the full
range of M-stars) receive stellar fluxes that exceed the runaway
greenhouse threshold, and thus may lose substantial amounts of water
initially delivered to them.
We predict that M-star planets need
to initially accrete more water than Earth did or, alternatively, have
additional water delivered afterwards to remain habitable. Our findings
are also consistent with recent claims that Venus lost its water during
accretion.
Cornell University
The
habitable zone (HZ) is the region around a star in which liquid water
could exist on a planetary surface. Although most HZ studies have
focused on the main-sequence period, here we argue that the
pre-main-sequence HZ likely provides additional targets for observers.
The spatial distribution of liquid water and its change during the
pre-main-sequence phase of protoplanetary systems is important in
understanding how planets become habitable.
Such worlds are
interesting targets for future missions because the coolest stars could
provide habitable conditions for up to 2.5 billion years post-accretion.
Moreover, for a given star type, planetary systems are more easily
resolved because of higher pre-main-sequence stellar luminosities,
resulting in larger planet-star separation for cool stars than is the
case for the traditional main-sequence (MS) habitable zone (HZ). Using
1-D radiative-convective climate and stellar evolutionary models, we
calculate pre-main-sequence HZ distances for F1-M8 stellar types. We
also show that accreting planets that are later located in the
traditional MS HZ orbiting stars cooler than a K5 (including the full
range of M-stars) receive stellar fluxes that exceed the runaway
greenhouse threshold, and thus may lose substantial amounts of water
initially delivered to them.
We predict that M-star planets need
to initially accrete more water than Earth did or, alternatively, have
additional water delivered afterwards to remain habitable. Our findings
are also consistent with recent claims that Venus lost its water during
accretion.
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