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Protecting Life on the Early Earth

Kappa Ceti is a young star — 400 to 600 million years old — in the constellation Cetus (the Whale). It’s a tremendously active place, its surface disfigured by starspots much larger and more numerous than we find on our more mature Sun. In fact, Kappa Ceti hurls enormous flares into nearby space, ‘superflares’ releasing 10 to 100 million times the energy of the largest flares we’ve ever observed on the Sun. What would be the fate of planets around a star like this?

The question is directly relevant to our own system because Kappa Ceti is a G-class dwarf much like the Sun, giving us a look at what conditions would have been like when our own system was forming. The calculated age of the star, extrapolated from its spin, corresponds to the time when life first appeared on the Earth. Thus we’re seeing a model of our distant past, one that makes it clear that a magnetic field is an essential for planetary habitability.

The violent activity on the surface of Kappa Ceti is driving a steady stream of plasma into space, a ‘stellar wind’ that is fifty times stronger than what we observe from the Sun. A planet without a strong magnetic field would potentially lose most of its atmosphere in this maelstrom. Lead author Jose-Dias do Nascimento (Harvard-Smithsonian Center for Astrophysics) and team note in the paper on this work that the 400 to 600 million year time frame in stellar age also corresponds to the time when Mars lost its liquid water some 3.7 billion years ago.

Understanding the interactions between the stellar wind and the surrounding planetary system, then, helps us get a read on the early history of our own system. From the paper:

A key factor for understanding the origin and evolution of life on Earth is the evolution of the Sun itself, especially the early evolution of its radiation field, particle and magnetic properties. The radiation field defines the habitable zone, a region in which orbiting planets could sustain liquid water at their surface (Huang 1960; Kopparapu et al. 2013). The particle and magnetic environment define the type of interactions between the star and the planet. In the case of magnetized planets, such as the Earth that developed a magnetic field at least four billion years ago (Tarduno et al. 2015), their magnetic fields act as obstacles to the stellar wind, deflecting it and protecting the upper planetary atmospheres and ionospheres against the direct impact of stellar wind plasmas and high-energy particles (Kulikov et al. 2007; Lammer et al. 2007).

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Image: In this artist’s illustration, the young Sun-like star Kappa Ceti is blotched with large starspots, a sign of its high level of magnetic activity. New research shows that its stellar wind is 50 times stronger than our Sun’s. As a result, any Earth-like planet would need a magnetic field in order to protect its atmosphere and be habitable. The physical sizes of the star and planet and distance between them are not to scale. M. Weiss/CfA.

The researchers used spectropolarimetric observations — measuring the optical properties of polarized light at different wavelengths — to analyze Kappa Ceti’s magnetic fields, combining these with models of stellar winds. Data were collected using a spectropolarimeter at the 2-meter Bernard Lyot Telescope (TBL) of Pic du Midi Observatory in the French Pyrenees.

Working with the magnetic properties of the young Earth and factoring in the strength of the young Sun’s plasma outflows allowed the team to estimate the size of the early Earth’s magnetosphere, which is found to be one-third to one-half as large as it is today. “The early Earth,” says do Nascimento, “didn’t have as much protection as it does now, but it had enough.”

The paper is do Nascimento et al., “Magnetic field and wind of Kappa Ceti: towards the planetary habitability of the young Sun when life arose on Earth,” accepted for publication at The Astrophysical Journal (preprint). A CfA news release is also available.

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Comments on this entry are closed.

  • RobFlores March 17, 2016, 11:44

    The Earth’s Magnetic field is very strong and we can thank…..Theia.

    There is a theory is that when Theia crashed against the larger earth, its core merged with that of the Young Earth, but a lot of the upper crust was ejected into space of which most became the material source for our moon’s formation. So it is this jumbo core (while portions of it remain liquid)
    and our rotation that gives us the extra protection.

    Looking at the implications of article, and assuming the Theia assumption
    is correct. What would an Earth, without a Theia impact look like?

    1) The Earth would not have the Ocean basins, and therefor would be
    mostly a water world (except for volcanic mini-continents)

    2) I don’t see how proto-life would survive in a “calm pool of chemicals”
    with the extra solar radiation reaching the surface due to a weaker magnetic field. I think it’s a longer odds, that life arises on Earth. Theia may have
    sterilized Earth for a time, but he chemicals of life where there when things
    settled down.

    3) Did Theia add to the Earth’s rotation rate or not? If it did give the
    Earth a 10-11 hour rotation rate, w/0 Theia what would the Earth’s rate of
    rotation be Today.?

    4) what would be the atmospheric pressure be today? quite a bit lower
    I would think.

    It look to me as it without Theia, The period where the Earth can harbor
    life and give rise to complex animals is significantly shorter. If we are looking at Drake Equations factors, maybe this one needs to be put in.

    • Michael March 17, 2016, 13:01

      ‘The Earth’s Magnetic field is very strong and we can thank…..Theia.

      So it is this jumbo core (while portions of it remain liquid)
      and our rotation that gives us the extra protection…Looking at the implications of article, and assuming the Theia assumption
      is correct. What would an Earth, without a Theia impact look like?

      1) The Earth would not have the Ocean basins, and therefor would be
      mostly a water world (except for volcanic mini-continents).

      Mars has quite a height variation as does Venus with no theoretical impacts.

      2) I don’t see how proto-life would survive in a “calm pool of chemicals”
      with the extra solar radiation reaching the surface due to a weaker magnetic field. I think it’s a longer odds, that life arises on Earth. Theia may have sterilized Earth for a time, but he chemicals of life where there when things settled down.

      There was a very thick atmosphere of CO2 for quite a while, so would have afforded a lot of protection.

      3) Did Theia add to the Earth’s rotation rate or not? If it did give the
      Earth a 10-11 hour rotation rate, w/0 Theia what would the Earth’s rate of
      rotation be Today.?

      I think it gave Earth a 5 hour rotation period.

      4) what would be the atmospheric pressure be today? quite a bit lower
      I would think.

      Without the impact I would think it would be higher.

      ‘It look to me as it without Theia, The period where the Earth can harbor
      life and give rise to complex animals is significantly shorter. If we are looking at Drake Equations factors, maybe this one needs to be put in.’

      The Theia impact would have been a surface sterilisation event for quite a while, but if bugs were on the surface they could have been flung into near Earth space returning and surviving when the conditions became cooler.

    • Scott Gordon March 18, 2016, 6:47

      Hi RobFlores
      Re: your points :

      1. Ocean basins on Earth have nothing to with giant impacts. They’re created and destroyed continuously by plate tectonics. The Theia impact if it happened, smashed the part and it reformed itself. There was no impact crater (and it would not have survived until now).

      2. Life probably arose on Earth in geothermal systems underground or on the seafloor so solar radiation shouldn’t have been a big issue. It doesn’t take much rock to absorb it.

      3. When you smash too large rotating objects together, you get another large rotating object (+ debris) but the rotation depends on total angular momentum, which is mostly from the relative motion and place of impact of the two objects before they collided, not from their original rotation (eg. did Theia hit Earth on the left or right ? North or South ?) so it would be hard to work out.

      Cheers

    • Eniac March 22, 2016, 22:11

      3) Mars’ rotation rate is not so much different from Earth’s, which proves that, at least for that part, Theia is not needed.

  • Dave Moore March 17, 2016, 13:28

    I wonder how Venus kept its atmosphere. It still has 3 bars of Nitrogen, so while it might have lost its water via Hydrogen escape and oxidation, it kept all its Nitrogen.

    • Stephen March 17, 2016, 19:59

      Maybe we could use some of this Venusian nitrogen to someday build atmospheres for Mars ans Selene/Luna.

      • Michael March 18, 2016, 16:07

        I would think it better to build large habitats in orbit around mars, there are two moons for materials, and then look down upon Mars as a sight to behold.

    • andy March 18, 2016, 19:00

      That depends on how much nitrogen is present in the interior of Venus. On Earth, there may well be several atmosphere’s worth of nitrogen locked up in the core and mantle, while Venus seems to have undergone rather more outgassing than the Earth has. A simple comparison of the amount of nitrogen in the atmospheres of Venus and Earth may give a misleading impression.

      • Michael March 19, 2016, 9:20

        I would have thought that after the moon formation event the Earth would have been degassed significantly.

  • Joe March 17, 2016, 13:51

    It would be nice if this article went on to mention WHY the earth’s magnetic field increased in strength over the eons. The fact that earth’s magnetosphere got stronger implies that the same thing could happen on other worlds. So even for a planet with a magnetosphere too weak to block solar flares now, life still might get started at some point in the future if the magnetosphere gets stronger.

  • Ashley Baldwin March 17, 2016, 15:54

    Hydromagnetodynamic fields are driven by planetary speed of rotation and convection in an outer liquid iron /nickel core . The liquid core in turn is driven by heat, left overs of formation in conjunction with decay of its natural radioactive isotope load which will be dependent on its mass. Whether that is due to a large impact event ( which may have driven off the last vestiges of Earth’s primordial H/He atmosphere left over by the stellar wind, to be replaced by plate tectonic driven vulcanism driven by convection in the outer mantle ) or just natural accretion from the protoplanetary disk the fact is that protective magnetic fields are to a large extent dependent on the size and rotation rate of a nascent planet. Rotation rates are determined by many factors other than just impact events so I think the reassuring outcome of this study is that large enough planets will likely develop a magnetic field as long as they are not so large that internal pressures prevent outer core convection ( and not helping mantle convection too) . To my knowledge , assuming an Earth like isotope density the optimum mass for a terrestrial planet in terms of developing a magnetic field is twice that of Earth with the rest dependent on rotation . So important as the Theia impact may have been , there are many of other ways to a protective magnetic field .

  • Andrew Palfreyman March 17, 2016, 17:04

    Poor Mars, but mysterious. Twice as distant from Sol as is Earth, and thus one quarter of the solar flux. And yet it still got atmospherically ripped up. The physics of magnetosphere formation is clearly very important to comprehend.

  • Ashley Baldwin March 17, 2016, 17:14

    As an appendix , plate tectonic driven vulcanism can extend over billions of years as illustrated by Earth and much much longer still in larger terrestrial planets . This would allow them to replace any atmosphere lost to even the extended stellar activity of pre and newly post main sequence M dwarfs , which could be crucial in allowing the eventual development of life though at a much later stage than seen with the Earth around our generally well behaved Sun. Better still thick atmospheres can resist the synchronising effect of even the close in orbits required for Habitable zone planets around M dwarfs . Still allowing the reasonable rotation rates necessary for magnetic field production, which apart from protecting the atmosphere also assist it in resisting high energy stellar radiation and cosmic rays. An extreme example of this effect described by Leconte last year is Venus. Despite the Sun’s gravitational attempts to synchronise it , not only has it resisted but actually rotates in a retrograde direction thanks to its 90bar atmosphere . Nasty for life obviously , pressure wise alone never mind the 400*C temperatures . Even atmospheres of less than a more manageable few bar have been shown to resist the effects of much smaller M dwarfs despite their closer proximity . The only unresolved issue then is the impact of high G gravity on life . Apart from extensive micro G study over the years of manned space flight culminating in the ISS , the only other assessment of Gravity’s influence on life has been during the 1/6 G moon landings and unpleasant short term high G rides on astronaut testing large centrifuges . What effect would the 1.5 or 2 G plus of a super terrestrial planet have on life ? Who knows. As with extraterrestrial life itself probably unknowable until observed.

    • Eniac March 22, 2016, 21:46

      “What effect would the 1.5 or 2 G plus of a super terrestrial planet have on life ? Who knows”

      I think this is quite clear. On microscopic life, there would be no effect at all. On maritime life, also no effect at all. Macroscopic land life would be somewhat more limited in size, meaning the equivalent of their largest dinosaurs would be half the size of ours, at 2 g. Trees would be half as tall, etc, etc.

      It’s a simple matter of physics. Reduce size to half, weight is reduced by a factor of 8, bone and muscle strength by a factor of 4, leaving room for increased gravity by a factor of 2. For all organisms that need to carry weight. Microscopic organisms and maritime organisms to not have to carry weight, so they can easily live under 100’s of g.

    • Eniac March 22, 2016, 21:53

      “Nasty for life obviously , pressure wise alone never mind the 400*C temperatures”

      Actually, the pressure would be no problem at all, as the existence of plenty of life in the deep ocean proves beyond doubt.

      Temperature is more of a problem, although I understand that some of the thermal vents where you do find life get pretty close to 400 C. I doubt, though, any organism based on Earthly biochemistry could actually live at that temperature. I think the thermal vent creatures only live close-by, where it is cooler. But alien chemistry could be different, and then all bets are off until a few thousand degrees when nothing stays liquid and everything turns into a plasma.

    • Eniac March 22, 2016, 21:55

      What is really preventing life on Venus is, of course, the lack of liquid water. There is very little water, and none of it is liquid, I think.

  • Ronald March 18, 2016, 6:27

    Interesting and relevant article. However, it only considers the essential planetary characteristics in relation to protecting early life, and not differences in stellar characteristics.
    What I mean is: would somewhat cooler solar type stars, such as spectral types G5 – G9, have fewer and/or smaller flares and/or less stellar wind in their early phases?
    More generally: what is the relationship between stellar spectral type (which in turn correlates with mass, color, temperature, luminosity) and flares for solar type stars (roughly F9 – K0)? I know that M dwarfs tend to have huge flares in their early lives, but how is that for solar type stars?

    It may turn out, that there exists an optimal combination of stellar type and planetary size/type with respect to long-term habitability, e.g. (purely as an arbitrary example) a 1.5 Me planet, 36 hour rotation, around G9 star.

  • DJ Kaplan March 18, 2016, 13:12

    Will we ever know if there are any Earthlike planets with strong magnetic fields? If this is rare in the ‘verse, then so is life…

  • FrankH March 18, 2016, 14:58

    The loss of atmosphere on Mars isn’t that mysterious when you look at the number of huge impacts that it has endured (in particular, the North Polar basin). A magnetic field would not have helped if sections of the atmosphere were being heated to escape velocity by impacts. Not having a magnetic field just made things worse.

  • RobFlores March 18, 2016, 17:49

    Regarding Mars’ evolution:

    There was a gigantic impactor that created the Mars hemispheric
    dichotomy. The impactor may have been as large as earth’s moon.
    My impression was that whatever Mars had going
    in terms of habitability this impactor probably shortened
    substantially.

  • JonW March 18, 2016, 22:54

    Is there any news about astronomical/spectrographical/other techniques that could detect magnetic fields in exoplanets? Seems like a very important question to know the answer to for anyone interested in the likelihood of life arising elsewhere.

    • Michael H. March 19, 2016, 21:12

      Here is an article where scientists at Moscow University estimate the magnetic field of an exoplanet:

      https://www.sciencedaily.com/releases/2014/11/141120141800.htm

      • DJ Kaplan March 23, 2016, 13:04

        The only other planets in our solar system that have magnetic fields are gas giants, similar to the exoplanet discussed here. But so far we are the only rocky planet (or even large moon) with magnetism. It may be a game changer, relative to ET life or colonization of space.

  • Michael March 19, 2016, 1:11

    We could give Mars its magnetic field back, we could create a magnetic field with superconductors at the cold poles and with enough energy. The planet would re-magnetise and a smaller energy input would be required to maintain it.

  • Eniac March 22, 2016, 22:01

    In our solar system, a magnetic field is clearly unnecessary to retain atmosphere. For proof look at Venus: No internal magnetic field, super-thick atmosphere. QED.

    • DJ Kaplan March 23, 2016, 13:00

      True, Eniac, but a strong magnetic field may be essential for the evolution of life as we know it.

      • Eniac March 25, 2016, 18:36

        This statement is pointlessly generic unless you propose some specific mechanism by which it would be true.

        • DJ Kaplan March 29, 2016, 17:49

          The geomagnetic field keeps out damaging solar and cosmic radiation, which has been proven to damage DNA. A fairly well-established mechanism, which is why I assumed you knew of it.