Solar Wind Sputtering - Revision history

RichardWSmith: /* Atmospheric Loss of Light Gases */ Fixed typo.

2025-08-16T09:25:17Z

Atmospheric Loss of Light Gases: Fixed typo.

RichardWSmith: /* Bibliography */ Added another reference.

2025-08-09T04:28:32Z

Bibliography: Added another reference.

RichardWSmith: /* Isotope Ratios */ Isotope ratios of noble gases suggest sputtering is over rated.

2025-08-09T04:26:50Z

Isotope Ratios: Isotope ratios of noble gases suggest sputtering is over rated.

RichardWSmith: /* Solar Wind Sputtering */ Reminds that this is slow, but over billions of years it adds up.

2025-08-03T14:45:33Z

Solar Wind Sputtering: Reminds that this is slow, but over billions of years it adds up.

RichardWSmith: Added link

2025-08-03T14:39:25Z

Added link

RichardWSmith: /* Solar Storms */ Added link.

2025-07-30T13:44:21Z

Solar Storms: Added link.

RichardWSmith: /* Rate of Escape to Space */

2025-07-29T18:11:24Z

Rate of Escape to Space

RichardWSmith: /* Rate of Escape to Space */ improved grammar

2025-07-29T18:10:08Z

Rate of Escape to Space: improved grammar

RichardWSmith: /* Rate of Escape to Space */

2025-07-29T18:08:59Z

Rate of Escape to Space

RichardWSmith: /* Rate of Escape to Space */

2025-07-29T18:07:54Z

Rate of Escape to Space

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 Mars has a surface gravity that it should be able to hang on to heavier molecules such as [[oxygen]] (O<sub>2</sub>), [[nitrogen]] (N<sub>2</sub>), [[carbon monoxide]] (CO), [[carbon dioxide]] (CO<sub>2</sub>), and heavier gases.
-Mars originally had a thick atmosphere of 3 or 4 bar, but now is a near vacuum (0.6 bar).  What caused the atmosphere to be stripped away?  (Note: some scientists think that Mars could not have such a thick early atmosphere, but it is hard to explain how Mars could have had running water ~4 to 5 billion years ago without it.  Note that then, the Sun was only 70% as warm as it is now, so running water on an early Mars is doubly hard to explain.)
+Mars originally had a thick atmosphere of 3 or 4 bar, but now is a near vacuum (0.006 bar).  What caused the atmosphere to be stripped away?  (Note: some scientists think that Mars could not have such a thick early atmosphere, but it is hard to explain how Mars could have had running water ~4 to 5 billion years ago without it.  Note that then, the Sun was only 70% as warm as it is now, so running water on an early Mars is doubly hard to explain.)
 Note that Owen & Tobias calculated that Mars had a 10 bar CO2 atmosphere in a paper in Icarus #166, but this is an outlier, most scientists prefer thinner atmospheres.<ref>Owen, Tobias; Bar-Nun, Akiva (1 August 1995). "Comets, impacts, and atmospheres". Icarus. 116 (2): 215–226.</ref>

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 ==Bibliography==
-"The Atmosphere and Climate of Mars", Edited by Robert M. Haberle, et al, Cambridge Planetary Science, ISBN 978-1-107-01618-7.  See Chapter 15: "Solar Wind Interaction & Atmospheric Escape".
+"The Atmosphere and Climate of Mars", Edited by Robert M. Haberle, et al, Cambridge Planetary Science, ISBN 978-1-107-01618-7.  See Chapter 15: "Solar Wind Interaction & Atmospheric Escape".  See also Chapter 17: "Evidence for a Different Atmosphere & Climate".
 ==References==

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 ===Isotope Ratios===
 Many gases are made of atoms with more than one [[Isotopes|Isotope]].  Since these differ in mass, lighter isotopes are less dense and tend to rise to the top of the Martian atmosphere.  These are more subject to sputtering, and thus, lighter isotopes tend to be lost more quickly than heavier ones.  By measuring the ratios between light and heavier isotopes, scientists have estimated that about 1/3 of the Martian carbon dioxide has been lost to space in the last 5.5 billion years.
 (Some recent studies suggest that this might be higher, over 50%.  Note that molecules and atoms with lower mass, will have a higher % of them lost to space.  Mars will have kept a higher % of heavier molecules like CO<sub>2</sub>)
-These studies are difficult because we do not know the initial isotope ratios, and because we do not know if the 'clock' was reset by comet impacts refilling the atmosphere with new batches of volatiles.
+These studies are difficult because we do not know the initial isotope ratios, and because we do not know if the 'clock' was reset by comet impacts refilling the atmosphere with new batches of volatiles.  Also if Mars had an atmospheric pressure of 0.5 to 1.0 bar in the Noachian, then sputtering and other forms of atmospheric escape can account for the current pressure.  If Mars had 4 or 5 bar then, then sputtering is not capable to removing that much (so it must have been absorbed into the crust).
 ===Direct Measurements by Orbiting Spacecraft===

← Older revision		Revision as of 14:45, 3 August 2025
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	Sputtering should allow gases to escape from heavy planets, but Venus (also with no magnetic field) has a solar wind more than 4.4 times that of Mars and has not lost much atmosphere to solar wind sputtering. This is far less than predicted, so our models need to be adjusted.		Sputtering should allow gases to escape from heavy planets, but Venus (also with no magnetic field) has a solar wind more than 4.4 times that of Mars and has not lost much atmosphere to solar wind sputtering. This is far less than predicted, so our models need to be adjusted.
		+
		+	Sputtering results in a slight increase in the rate of atmospheric loss, but over hundreds of millions or billions of years it becomes significant.

	==Detailed Discussion==		==Detailed Discussion==

← Older revision		Revision as of 14:39, 3 August 2025
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−	Solar Wind Sputtering is a process where the solar wind slowly strips away the atmosphere of a planet without a strong magnetic field. It is thought to have removed about 1/3 of Mars' early atmosphere. See [[Atmospheric loss]] for a full description of what has happened to Mars' originally thick atmosphere.	+	Solar Wind Sputtering is a process where the solar wind slowly strips away the atmosphere of a planet without a strong magnetic field. It is thought to have removed about 1/3 of Mars' early atmosphere.
		+
		+	See [[Ancient Atmosphere]] and [[Atmospheric loss]] for a full description of what has happened to Mars' originally thick atmosphere.

	==Overview==		==Overview==

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 ===Solar Storms===
-Observations of young stars suggest that Coronal Mass Ejections (CME) or solar storms were more common, and more powerful with our young sun.  However, early in Mars' history, it had a magnetic field protecting it.  It is debated if the early solar storms would have had an outsized effect on the rate of Martian atmospheric loss, or if the magnetic field lasted long enough to cancel this effect.
+Observations of young stars suggest that [[Coronal Mass Ejections]] (CME) or solar storms were more common, and more powerful with our young sun.  However, early in Mars' history, it had a magnetic field protecting it.  It is debated if the early solar storms would have had an outsized effect on the rate of Martian atmospheric loss, or if the magnetic field lasted long enough to cancel this effect.
 Modern solar storms are expected to increase the rate of atmospheric loss, but the rate of the increase has not been well measured.

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 ===Rate of Escape to Space===
-Geologic models suggest Mars' magnetic field protected the atmosphere for the first 1.8 billion years of Mars lifetime. (This is longer than previous estimates based on MAVEN data.). Some studies suggest that it may have lasted 500 million years longer, or stopped then restarted at least once.<ref>https://science.ubc.ca/news/ubc-researchers-establish-new-timeline-ancient-magnetic-field-mars</ref>
+Studies suggest Mars' magnetic field protected the atmosphere for the first 1.8 billion years of Mars lifetime. (This is longer than previous estimates based on MAVEN data.). Some studies suggest that it may have lasted 500 million years longer, or stopped then restarted at least once.<ref>https://science.ubc.ca/news/ubc-researchers-establish-new-timeline-ancient-magnetic-field-mars</ref>
 Recent measurements estimate that the rate of Martian atmospheric loss (from all sources, not just sputtering), is about 2.5 kg / second or ~79,000 tonnes per year.  (For comparison, the mass of the Earth's atmosphere is 5,150,000,000,000,000 tonnes.)

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 This paper suggests that while a strong magnetic field protects the atmosphere, a very weak one is actually worse than no magnetic field at all.  Thus, if Mars' magnetic field collapses partially and remained weak for a long time, it could explain the higher than expected atmospheric loss. <ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JA026945</ref>
-Note that Earth and Venus are both losing a bit under a kg of mass per second from atmosphere escape, and Mars is losing about 2.5 kg/s.  So Mars is losing mass about 3 times faster, but not orders of magnitude more quickly.
+Note that Earth and Venus are both losing a bit under a kg of mass per second from atmosphere escape, and Mars is losing about 2.5 kg/s.  So Mars is losing mass about 3 times faster than Earth, but not orders of magnitude more quickly.
 If terraformers were to somehow give Mars a 1 bar atmosphere (and didn't give it an artificial magnetic field which is much easier) it would take at least 500 million years for sputtering to reduce the atmosphere back down to its current near vacuum.