Nearby star is loaded with planets

A nearby star that’s been a staple of sci-fi and sci-fact for years may be loaded with planets, including at least one that may be able to support liquid water on the surface:

Digital Trends — The star in question is Tau Ceti, only 12 light-years from Earth and visible to the naked eye. The planets surrounding the star are estimated to be two to six times bigger than earth, with one in particular measuring five times the size of our home planet. Said planet is lying in what’s commonly known as the star’s “Goldilocks Zone” – a position that is neither too hot nor too cold, but instead exactly the right environment to support the prospect of liquid surface water, and therefore, life.

It took information collated from more than 6,000 observations from three telescopes located in Hawaii, Chile, and Australia to discover the planetary system, believed to be the lowest-mass solar system detected yet. The system was discovered using a sensitive process known as the “radical velocity method,” which searches for a “wobble” in a star’s movement caused by the gravitational pull of orbiting planets. According to Professor Steve Vogt of the University of California at Santa Cruz, who is part of the research team responsible for the discovery, uncovering the planets “is in keeping with out emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets. They are everywhere, even right next door.”


  1. Johnny Vector says

    Er, that’s “radial velocity”, not “radical”.

    And it looks like someone’s breaking embargo on this, since the paper isn’t published yet. Still, cool.

  2. says

    I like the way the media have been describing it as “habitable” when it’s 5x the size of earth. I guess it might be “habitable” in the same sort of sense that The Moon is habitable – if you take an earth-like environment along with you, including a robot to help you crawl around in the gravity. I.e.: not habitable at all.

  3. thebookofdave says

    Radial velocity detection is no longer radical, quickly becoming a staple of astronomy. But it’s no less cool.

  4. aziraphale says

    This planet is said to have 5 times the mass of Earth. If has the same density, its surface gravity would be 70% higher than Earth’s. But it could be less. In our system Neptune with a mass of 14.5 Earths only has 88% of Earth’s gravity.

    In any case I think the excitement is mostly about the possibility that organisms with our body chemistry (and intelligence?) could live there, not that we ourselves could.

  5. slc1 says

    Re azirphale
    But it could be less. In our system Neptune with a mass of 14.5 Earths only has 88% of Earth’s gravity.

    This is poorly stated. What is apparently meant is that the gravitational acceleration as measured at the surface of Neptune is only 88% of the gravitational acceleration measured at the surface of the earth. The gravitational acceleration as measured from, say 50,000 miles from the center of Neptune would be 14 times the gravitational acceleration as measured from 50,000 miles from the center of the earth.

  6. says

    The surface gravity on a 5X earth mass world is an interesting math problem, it’s dependent on density as that changes the radius of the surface point. It’s unlikely a planet that small and that close would be a hydrogen/helium gas dwarf, it wouldn’t last. But it could be a methane dwarf or very low density substances, which would mean the gravity at it’s surface might be LESS than ours theoretically, or it could be roughly earth density in which case the surface gravity would be (Back of a virtual enveleope here) … I think between 1.5 and 2x g — Not sure on that though.

  7. aziraphale says

    slc1: in the context of the discussion it should have been clear that I was talking about surface gravity. That’s the figure that’s relevant to discussions of habitability.

  8. aziraphale says

    re: Stephen “DarkSyde” Andrew “(Back of a virtual envelope here)”

    I prefer to use the Windows calculator which is always to hand – unless you use one of those minority operating systems. It even has a cube root button.

    It’s not complicated. Choose units in which Earth’s mass, radius and gravity are all equal to 1. Let the new planet’s mass, radius and gravity be M, R and g, and assume its density is the same as Earth. Then:

    Mass varies as volume which varies as the cube of radius, so M = R cubed and R = (cube root of M) = (cube root of 5) = 1.7 approx.

    Also g varies as M/(R squared) which varies as R, so g = 1.7

    which is where I got my 70%.

    Your virtual envelope is correct but imprecise. But then, so are the data.

  9. Amphiox says

    A surface gravity of 1.7X earth’s is one where it is conceivable that humans could in fact survive for extended periods, after acclimating, without significant technological aid.

  10. robb says

    gravitational acceleration at surface of planet is
    a=(GM) / R^2 (gravitational constant G, mass M and radius R
    mass is M= p 4/3 π R^3. (average density p and radius R)

    combining a nd M yields

    a=G(p 4/3 π R^3)/R^2= Gp(4/3)πR

    acceleration is proportional to density times radius.

    if the new planet had the same density, but 5x radius, the surface acceleration would be 5x larger.

    for instance, Neptune has an average density of 1640 kg/m^3. earth density is 5540 kg/m^3. Neptune radius is 2.47×10^7m and earth radius is 6.4×10^6m , which gives surface gravity of Neptune 1.14 times the surface gravity of Earth. so even though Neptune is much larger than Earth, it’s density is less so the surface gravity isn’t too different from Earth’s.

  11. Abdul Alhazred says

    If the habitable planet has an ocean of liquid water and otherwise the right chemicals, life can develop there and it doesn’t matter what the surface gravity is.

    “Habitable” doesn’t mean people can live there.

  12. says

    Even if the planet had a surface gravity of about 1g, it is very, very unlikely that the planet still would be habitable. Earth itself has been habitable by modern Terran life for barely 500 million years — one ninth of its existence — and even so, there were gaps when human survival would have been very difficult.

    Does the planet have a 20% oxygen atmosphere? A complete absence of toxic gases like hydrogen sulfide, carbon monoxide and ammonia? Almost certainly, humans could not derive nutrition from alien life forms; can the planet’s soil support Terran crops? Would they be fit for human consumption, or would they be tainted by high levels of toxic metals or poisonous salts? What are the chances that native protein analogues might cause allergic reactions and related fatalities?

  13. says

    @Abdul Alhazred #11 – Unfortunately, when most people think of a “habitable planet,” they immediately assume human habitable. You can thank Star Trek for that: “That is an M-class planet, so we can easily beam down without the need for life support and safely eat the food and drink the water. Oh, and the remarkably humanoid natives will all speak English, everywhere on the planet.”

  14. StevoR, fallible human being says

    Tau Ceti is thought to be an older metal poor star :

    which may complicate things here regarding availability of metals and chances of planetary habitability especially for humans.

    Superluminous (beyond merely brilliant) discoveries and can’t wait to learn more but still a whole lot of questions and , I gather, still be be completely confirmed.

    @ 4. aziraphale : “In our system Neptune with a mass of 14.5 Earths only has 88% of Earth’s gravity.”

    Really? :

    “Neptune is both smaller and denser than its “twin” Uranus – so while it would take 14 Earth’s to match Uranus, but it would take 17 Earth’s to match Neptune.”
    – P. 57, ‘The Sky at Night’, Patrick Moore, WW. Norton & Co, 1986.

    Unless that figure has been revised since and I haven’t heard about it? Pretty sure Neptune has closer to 17 Earth masses than 14. Wikipedia for another source says Neptune is 17.1 earth mass.

    Ouranos does have 14 earth mass tho’ so was that the one you meant?

  15. StevoR says

    This space dot com article here :

    Notes the yet to be confirmed nature of the Tau Ceti planets too :

    The five planets remain candidates at this point and will not become official discoveries until they’re confirmed by further analysis or observations. And that’s not a sure thing, researchers said.

    “I am very confident that the three shortest periodicities are really there, but I cannot be that sure whether they are of planetary origin or some artifacts of insufficient noise modelling or stellar activity and/or magnetic cycles at this stage,” Tuomi said, referring to the potential planets with orbital periods of 14, 35 and 94 days (compared to 168 days for the habitable zone candidate and 640 days for the most distantly orbiting world).

    “The situation is even worse for the possible habitable zone candidate, because the very existence of that signal is uncertain, yet according to our detection criteria the signal is there and we cannot rule out the possibility that it indeed is of planetary origin,” he added. “But we don’t know what else it could be, either.”

    Wonder when these worlds are most likely to be confirmed or disproven for sure? Does anyone know?

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