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The Sun and Earth in the distant future
The Sun and Earth in the distant future
Evolution of the Sun (schematic)
Evolution of the Sun (schematic)
The Sun and Earth in the distant future Evolution of the Sun: With
The Sun and Earth in the distant future Evolution of the Sun: With
The Sun and Earth in the distant future Fate of the Earth – doomsday
The Sun and Earth in the distant future Fate of the Earth – doomsday
The Sun and Earth in the distant future Might the Earth be saved after
The Sun and Earth in the distant future Might the Earth be saved after
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The Sun and Earth in the distant future

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1The Sun and Earth in the distant 9angular momentum is NOT conserved: tidal
future. Outline: Introduction Evolution of interaction and dynamical friction act to
the Sun Fate of the planets (and us) The decrease it. Assuming the Sun is
end-game. Will the Sun look like this? non-rotating on the RGB (conservation of
(K-P Schr?der & R C Smith, MNRAS, its AM), the orbital motion of the Earth
submitted). 3-D simulation of a pulsating raises a tidal bulge on the Sun that pulls
red giant the Earth back in its orbit. In addition,
(http://www.lcse.umn.edu/research/RedGiant the Earth is orbiting through the extended
). chromosphere of the Sun, giving rise to
2The Sun and Earth in the distant drag. Detailed computations give:
future Introduction. Global warming 10The Sun and Earth in the distant
climate change. The Sun’s luminosity is future Fate of the Earth – doomsday!
slowly increasing – what will that do to Effect of mass loss. Earth’s orbit. Effect
us? On ZAMS, Lsun ~ 70% Lsun(now) – but of tides and drag. Sun’s radius.
geological evidence suggests Tearth ~ 11The Sun and Earth in the distant
constant for last 3-4 billion years Can future What happens to life, and when? The
the feedback mechanism that kept the Earth is swallowed ~0.5 million years
temperature constant in the past also do before the RGB tip, or about 7.59 Gy in
so in the future, and for how long? the future But increased solar irradiation
3The Sun and Earth in the distant acts much faster – even without increased
future What happened in the past? Early CO2, the rise in temperature will cause
atmosphere was rich in CO2 – kept Earth evaporation of the oceans to start – and
warm by strong greenhouse effect Clouds water vapour is another greenhouse gas A
may also matter – some evidence that CR moist greenhouse effect will continue
encourage cloud cover at low altitudes, until the oceans have boiled dry
leading to higher reflection and lower (Laughlin, Sky & Telescope, June 2007,
temperature; strong early solar wind may p.32) Solar UV will then dissociate the
have excluded galactic CR, leading to water molecules, and the hydrogen will
lower cloud cover and higher temperature escape, leaving the Earth a lifeless
CO2 gradually locked up in carbonates and dust-bowl The subsequent dry greenhouse
plants (limestone deposits contain about effect will raise the temperature further
70 atmospheres of it!) – so greenhouse until the Earth is essentially a molten
effect decreased as solar irradiation ball Timescale is ~1 Gy – so life will
increased (the Gaia effect) Current disappear long before the Earth does.
climate models suggest that including 12The Sun and Earth in the distant
biospheric (Gaia-type) effects may future Can we postpone the extinction of
actually increase CO2 production as life? Options: terra-forming Mars? Space
vegetation dies back – so feedback stations drifting out through the solar
probably won’t help in future. system? Colonise the Galaxy? None would
4Evolution of the Sun (schematic). The save more than a tiny fraction of life on
Sun and Earth in the distant future. Earth Move the Earth itself outwards?!
Detailed calculations made by Peter Serious proposal (Korycansky et al,
Schr?der, using modified Eggleton code. Ap&SpSci, 275, 349, 2001) to use
Expansion up Asymptotic Giant Branch. He Kuiper Belt objects in close fly-by to
flash. Core He burning. Sun expands up red nudge the Earth every 6000 years so that
giant branch. Core H exhausted. The Sun it moves out at just the right rate
now. Energetically possible, and could be
5The Sun and Earth in the distant technically possible in the near future (a
future Evolution of the Sun: No mass loss. few centuries) Very dangerous! But could
Log Rsun and Log Dplanets (Units: extend habitability of Earth for whole MS
Rsun(now)). Mars. Earth. Venus. Mercury. lifetime of Sun (~6 Gy) – a big gain.
All planets swallowed at RGB or AGB stage. 13The Sun and Earth in the distant
Sun. future What happens to the Sun? Textbooks
6The Sun and Earth in the distant say: Sun ends as white dwarf after
future Evolution of the Sun: With mass ejecting planetary nebula (PN) Our
loss. Solar wind mass-loss is negligible calculations show mass loss on AGB is
(~10-14 Msun/year). Mass loss is much relatively low (0.116 Msun) because most
greater at RGB and AGB stages. We use a of envelope lost on RGB PN usually emitted
new semi-empirical formula, calibrated by superwind as part of last thermal pulse
from globular cluster giants and nearby on AGB – but our calculations show only
galactic giants (Schr?der & Cuntz, 0.0075 Msun is lost in final pulse – much
ApJ, 630, L73, 2005 and A&A, 465, 593, less than a normal PN mass. So any PN
2007): where ? = 8?10-14 solar would be very tenuous and faint A final
masses/year. This leads to a loss of 0.332 thermal pulse after leaving the AGB causes
Msun by the tip RGB. final mass loss, and the expected final WD
7The Sun and Earth in the distant mass is 0.5405 Msun.
future Evolution of the Sun: With mass 14The Sun and Earth in the distant
loss. Mass loss ? weaker gravitational future Conclusions. The Earth is lost
pull – so the Sun expands a bit more, but eventually: engulfed by Sun 7.59 Gy in the
also the planetary orbits expand. If future Life might hang on for ~6 Gy*, but
angular momentum is conserved, then: where the ultimate future of the human race (if
rE is the radius of the Earth’s orbit at it survives) would need to be elsewhere *
time t and ?E is the (constant) orbital If the Kuiper Belt Object nudging scheme
angular momentum. At the tip RGB, the Sun worked – and then in fact the Earth itself
reaches a radius of 1.2 AU, but the might avoid engulfment.
Earth’s orbit has moved out to 1.5 AU. By 15The Sun and Earth in the distant
the time it gets to the AGB, the Sun has future Might the Earth be saved after all?
lost so much mass from its envelope that A planet with initial orbital radius 1.15
it expands less far, only to 0.7 AU, so AU or more will escape engulfment.
the Earth escapes: 16The Sun and Earth in the distant
8The Sun and Earth in the distant future Conclusions. The Earth is lost
future Evolution of the Sun: With mass eventually: engulfed by Sun 7.59 Gy in the
loss. Earth’s orbit. AGB. Sun: RGB. future (probably: certainly true in
9The Sun and Earth in the distant absence of human intervention) Life might
future Fate of the planets. So – it hang on for ~6 Gy, but the ultimate future
appears that Mercury and Venus get of the human race (if it survives) would
swallowed, but the other planets escape. need to be elsewhere. The Sun doesn’t even
Is that the whole story? No – orbital produce a proper planetary nebula!
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The Sun and Earth in the distant future

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