An artist impression of an exomoon orbiting an exoplanet, could the exoplanet's wobble help astronomers? (Andy McLatchie)

Astronomers Now Looking For Exomoons Around Exoplanets

Article Updated: 26 Apr , 2016
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[/caption]It looks like astronomers have already grown tired of taking direct observations of exoplanets, been there, done that. So they are now pushing for the next great discovery: the detection of exomoons orbiting exoplanets. In a new study, a British astronomer wants to use a technique more commonly associated with the indirect observation of exoplanets. This technique watches a candidate star to see if it wobbles. The wobble is caused by the gravitational pull of the orbiting exoplanet, revealing its presence.

Now, according to David Kipping, the presence of exomoons can also be detected via the “wobble method”. Track an exoplanet during its orbit around a star to see its own wobble due to the gravitational interaction between the exoplanet/exomoon system. As if we needed any more convincing that this is not already an ‘all kinds of awesome’ project, Kipping has another motivation behind watching exoplanets wobble. He wants to find Earth-like exomoons with the potential for extraterrestrial life…

If you sat me in a room and asked me for ten years over and over again: “If you were an astronomer, and you had infinite funds, what would you want to discover?“, I don’t think I would ever arrive at the answer: the natural satellites orbiting exoplanets.” However, now I have read an article about it and studied the abstracts of a few papers, it doesn’t seem like such a strange proposition.

David Kipping, an astronomer working at the University College London (UCL), has acquired funding to investigate his method of measuring the wobble of exoplanets to reveal the presence of exomoons, and to measure their mass and distance from the exoplanet.

Until now astronomers have only looked at the changes in the position of a planet as it orbits its star. This has made it difficult to confirm the presence of a moon as these changes can be caused by other phenomena, such as a smaller planet,” said Kipping. “By adopting this new method and looking at variations in a planet’s position and velocity each time it passes in front of its star, we gain far more reliable information and have the ability to detect an Earth-mass moon around a Neptune-mass gas planet.”

Kipping’s work appeared in the December 11th Monthly Notices of the Royal Astronomical Society and could help the search for exomoons that lie within the habitable zone. Of the 300+ exoplanets observed so far, 30 are within the habitable zones of their host stars, but the planets themselves are large gas giants, several times the size of Jupiter. These gas giants are therefore assumed to be hostile for the formation for life (life as we know it in any case) and so have been discounted as habitable exoplanets.

But what if these exoplanets in the habitable zone have Earth-like exomoons orbiting them? Could they be detected? It would appear so.

Prof. Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), added, “It’s very exciting that we can now gather so much information about distant moons as well as distant planets. If some of these gas giants found outside our Solar System have moons, like Jupiter and Saturn, there’s a real possibility that some of them could be Earth-like.”

Watch this space for an announcement of the first Earth-like exomoon to be discovered, at the rate of current technological advancement in astronomy, we could be looking at our first Earth-like exoplanet exomoon sooner than we anticipated…

Source: New Scientist, STFC


37 Responses

  1. Thunder Pig says:

    Wouldn’t the radiation fields around a “Jupiter-class” exo planet fry the surface of a potentially habitable exo-moon?

    Or is a standard magnetic field good enough to protect our aliens with a killer view featured in so many SciFi stories?

    Oh, and not even bringing up the whole tidal-lock thing that would kill a the development of a magnetic field.

    Still, this is very exciting. Imagine what we will be able to detect if we can get swarms of instruments into interplanetary space.

    Squee!!!

  2. Steve says:

    Thunder Pig,

    First off, being tidally locked to a planet would not hinder a bodies ability to develop a magnetic field. Take a look at europa and ganymede.

    Also, if the moon is far enough away from the exo planet, it may be far enough away from the radiation belt of the planet. Example, again ganymede.

    I would say that the odds of finding a moon that fits this criteria to be close to nil, but it is entirely plausible.

    However, Im interested to see if we are capable of detecting wobbles in the orbit of an object even as small as a hot jupiter around certain stars. I suppose its possible, but I d have my doubts.

  3. Dutch Delight says:

    But is there any possibility for us to detect the composition of atmospheres of these moons?

  4. Grinspoon says:

    Bring on the discover of the endor moon!

    Is it actually possible for a gas giant to have a moon that is an earth like planet?
    Or will it always be a moon that can at most support basic life? What implications are there to moons roations, sizes, and how often they face the sun?

  5. Jorge says:

    Hm… I’m confused by this.

    Wouldn’t the gravitational effects of the planet AND the moon on the star combine as if it were a single gravitation source, centered on the planet-moon system’s center of mass?

  6. Maxwell says:

    Capable of supporting life and capable of developing life are probably two different things.
    I’m positive that among the various forms of earth life, we could find some that would survive in pockets of the moons we know about. The question would be if a moon could exist around a giant planet, in some kind of stable condition, long enough for life to develop from scratch.

  7. maudyfish says:

    Not to change the subject but I wish this web site would do a special on spelling. There are so many new scientific words out there and. For some it may trivial but I think it would be worth it to comment.

    For example: exo-planet or exoplanet
    super nova or supernova
    exo-earths or exoearths
    jobian or Jovian
    mass less or massless
    redshift or red shift
    kiloparsec or kilo parsec

    Thanks

  8. Ilya says:

    Wouldn’t the gravitational effects of the planet AND the moon on the star combine as if it were a single gravitation source, centered on the planet-moon system’s center of mass?

    Yes, but that center of mass will not move in complete accordance with Kepler’s Laws. It will periodically speed up and slow down. Which is Kipping’s whole point.

  9. tacitus says:

    But is there any possibility for us to detect the composition of atmospheres of these moons?

    Sure, some day. We expect to be able to directly resolve Earth-sized exoplanets and smaller one day, so observing large moons should not be much more difficult than that, and given it’s the large moons that have atmospheres, we will probably get to see them one day.

    Sooner than that, I suspect we’ll be able to observe transiting moons of transiting planets. We can already subtract the light spectrum of a star from that of a planet in transit, so in theory if there is a large moon in just the right place (in front of the star but not in front of the planet) then there will be a tiny variation in the light spectrum we see, and then we should be able to subtract both the star’s signature and the planet’s and be left with just the moon’s, It’s likely our current equipment isn’t sensitive enough to detect this type of thing yet, but we’ve only been observing exoplanets for 10 years. Imagine what might be possible in another 10, 20, 50 years!

  10. Jason says:

    It would seem that if we could detect the very slight speeding up and slowing down of a planet moon system, that we could just a easly detect an earth sized planet going around a star. Which is thus far beyond our capibilities.

    Also ther are most likley mutiple moons for each planet, like Jupiter and saturn, which will muddy every thing up as well.

    Keep looking though, we called it impossible to find planests not so long ago.

    It seems more likley, that now we have imaged exoplanets that we could simply observe the planet itsself for wobles caused by exomoons.

  11. Kevin F. says:

    I’ve been expecting the possibility. We already are thinking there might be life of some odd manner on two of our gas giants – Titan and Europa. It would be perfectly reasonable to have a gas giant in the habitable zone having a life-bearing moon.

  12. Mang says:

    I continue to be amazed at the precision of measurement and analysis that can be produced. Just when you get used to the idea of exoplanets, we are on the verge of finding exoasteroids[1] and exomoons!

    [1] http://mangsbatpage.433rd.com/2008/08/hot-jupiter-trojans-most-finds.html

  13. Ilya says:

    It would seem that if we could detect the very slight speeding up and slowing down of a planet moon system, that we could just a easly detect an earth sized planet going around a star. Which is thus far beyond our capibilities.

    Sorry, but your intuition is wrong. An earth sized planet going around a star can not be detected (yet) because the wobble it induces is too small. If a gas giant planet induces a readily detectable wobble, the speed with which it rises and falls is much easier to measure. I have no links handy, but in several known multi-planet systems, planets’ gravitational influence on each other has already been found.

  14. Jason says:

    @ Ilya

    Yea, I would guess that the much shorter frequency of wobble induced by an earth sized moon would be easier to detect than that of a earth sized planet.

    The concept of a Titan or Europa like moon in the habitable zone of a star is exciting.

  15. Jorge says:

    Yes, but that center of mass will not move in complete accordance with Kepler’s Laws. It will periodically speed up and slow down. Which is Kipping’s whole point.

    Hm… still trying to wrap my head around this. So. I can think of only one way for this to happen: if the motion is such that we have to throw in relativity. Right?

    If so, surely the variations would be minute?…

  16. Silver Thread says:

    That’s no moon…..

  17. Some Guy says:

    ok, no ones brought this up, so i will
    any habitable moon that orbits a jupiter like planet beyond its radiation belt will likely have a pretty wide orbit. SO! that being said, this wide orbit could vary the moon’s distance from the host star by hundreds of thousands of kilometers within a very short period of time, would that not cause violent tidal swings on the surface, leading to aggressive weather, and putting any life there up against some tough odds?

  18. Dark Gnat says:

    Even if it does change, it probably wouldn’t be too gret of a change.

    Perhaps something like a global winter and summer. Titan might be a good model.

    I think this would be very possible, and a worthy effort!

  19. Ilya says:

    Now that I thought of it, I have to take back what I wrote about center of mass not moving in a simple Keplerian orbit. In short, I have no answer to Jorge’s question. All I can guess is that David Kipping is NOT expecting the star’s wobble to follow planet-moon center of mass, but to follow just the planet. Why, I do not know. And will try to find out.

  20. trux says:

    2 Ilya: I may be wrong, but perhaps the method relies on both measuring the gravitational wobble, and spectrographic analysis of planet transitions. In that case, although the travel of the center of the moon-planet system would be regular, there would be disaccords with the spectral transition measurements, which would then prove the moon presence. It surprises me though that the technology is already so sensitive that it could be detected. In any way, I’d love to read much more details about the methods used.

  21. As far as Moons, go, my only question centers on its “day.”

    Since its orbit would constantly take it within its parent planet’s shadow, wouldn’t this affect life for the worse?

    Also, as far as radiation belts go, both Ganymede and Europa orbit within its radiation belts, although the former is known to host a very strong magnetic field (unfortunately it does not block out all of Jupiter’s radiation).

    I think Titan would be a better example, of a large moon that orbits just within its parent worlds magnetic field (despite the fact that it lacks one itself).

  22. dollhopf says:

    As far as Moons, go, my only question centers on its “day.” Since its orbit would constantly take it within its parent planet’s shadow’

    Consider the Moon of the Earth. One could see the Moon in the shadow of the Earth just about hundered times throughout the whole 21st century.

  23. dollhopf says:

    If there were Exocreatures on an Exomoon of a Exoplanet, would it be easier for them to find Kepler’s Laws than it was for our astronomers? Are celestial mechanics more clearly seen, if one moves around a planet that moves around a star? The imagination makes me dizzy.

  24. Nexus says:

    It probably wouldn’t take them as long to work out their world isn’t the center of the universe as it took us.

  25. dollhopf says:

    I don’t know. Even if the moon that spins around the planet, and which itself spins around the sun togehter with its moon, would furthermore spin around its own axis (and not having one side turned toward the planet all the time like our satellite does).

    *#-)*

    How could they establish a celestial coordinate system so easily? And the seasons on Earth are caused by the change of the inclination during one revolution around the sun. But their seasons would change with every circle around their planet, maybe every month. Thus, what concept of time would they have developed?

  26. dollhopf says:

    “maybe every month”

    I mean OUR month of course. They probably would never have developed a time intervall like a month, which is caused by the observation of our moon.

  27. DJ Barney says:

    dollhopf …. “exocreatures” .. I like it ! That other word has become sort of … xenophobic ?

    I’m scrambling to keep up. Did we get over some kind of “hump” here ? Even if those exoplanets and now exomoons don’t harbour life, the techniques being developed will be invaluable.

  28. Jorge says:

    In short, I have no answer to Jorge’s question

    Oh. Too bad. I was really looking forward to learning something new here.

    So, either the experiment doesn’t make sense or there’s something here that’s eluding us. Ian, can’t you squeeze something else about this out of your sources?

  29. law mc says:

    would radiation really be that big a problem???

    the reason we are so susceptible to it is because we are shielded from it, but what if you were always exposed to it, wouldnt life have found ways to mitigate the problems that arise from it. After all, there are bacteria that are very radiation resistant on earth, so i dont think that idea is very strange at all.

  30. ScepticTim says:

    For those interested, I believe the paper that Ian refers to is arXiv:0810.2243v1 [astro-ph] 13 Oct 2008 “Transit Timing Effects due to an Exomoon” David M. Kipping

  31. Dark Gnat says:

    Now that some planets have been directly imaged, we could study those images over time to see if the planets themselves wobble. We wouldn’t have to look at the star to determine of the planet has moon(s).

    D. Clayton:

    If the moon is far enough away, and had an inclination relative to the planet, then it would only pass into the planet’s shadow on occasion. Even if it does regularly pass into the shadow, it be cyclic, and any life forms would have no trouble adapting.

  32. Frank Glover says:

    “How could they establish a celestial coordinate system so easily? And the seasons on Earth are caused by the change of the inclination during one revolution around the sun. But their seasons would change with every circle around their planet, maybe every month. Thus, what concept of time would they have developed?”

    If they watch things long enough, they’ll see patterns and cycles, just as humans did. Perhaps more importantly, such beings might not waste time on the kind of Ptolemaic, planet-centered Universe that western civilization on Earth did…

    Beings living on a body directly or indirectly circling one component of a double star might likewise be less inclined to believe the Universe literally revolves around them (unless the companion star was so distant and slow orbiting that it could be mistaken for a background star…)

  33. Yael Dragwyla says:

    dollhopf: ” ‘maybe every month’ I mean OUR month of course. They probably would never have developed a time intervall like a month, which is caused by the observation of our moon.” From the ever-changing relationship of their primary to their day-star — i.e., from synod to synod, as the primary and the day-star go from conjunction/New to opposition/Full — they could easily derive a time-unit based on the average length of a synod. As for days, that depends on whether they are tidally locked to their primary or not, the length of time it takes them to make one revolution about their primary, and the length of time it takes their primary to orbit their day-star. But they would have a day of some sort for a time-unit, and could peg their month/synod to that, or vice-versa, whichever was shortest.

  34. David Kipping says:

    Hello all,

    I have noticed some confusion about how the method works so I thought I would briefly summarise the idea. I’m very happy to see so many interesting discussions on the topic!

    The key point to bear in mind is that we are looking at the wobble of the planet, not the the wobble of the star. Every time a planet transits the star, it affords us information about the position and velocity of the planet. Even if the moon is too small to show up in the transit lightcurve, its effects on the host planet are not.

    Both the position and velocity of the planet will be perturbed by the presence of a moon. The spatial perturbation causes the planetary transit to occur slightly earlier or slightly later than expected. The velocity perturbation causes the transit duration to be slightly greater or slightly smaller. Remarkably, these effects can be minutes in magnitude.

    The two effects, called transit time variation (TTV) and transit duration variation (TDV) always exhibit a 90 degrees phase difference. In other words, we have a quite unique signature. In addition, the ratio of the two amplitudes allows for a determination of both the moon’s mass and its orbital distance from the host planet.

    It’s really fantastic to see so many people interested in exomoons. Who knows how common these exomoons may be and what potential for habitability they possess! Ultimately, the only way for us to answer these questions is to start looking!

    All the best and continue to ask questions!
    David

  35. Jorge says:

    Ah! NOW it makes perfect sense! Thanks for the explanation and the best of luck for the experiment.

  36. dollhopf says:

    DJ Barney told me:

    ‘”exocreatures” .. I like it ! That other word has become sort of … xenophobic ?’

    Yes, but I wonder about when the first manned spaceship will be designed to also carry weapons onboard. Will there once be a need to defend against or dominate over other “earthlings” during missions in space? Or will weapon systems once be integrated into space exploration vehicles or armament be foreseen in view of some “strange” (alien) events?

  37. ROCA says:

    Hi Ian,
    I have a huge interest in extrasolar moons as they solve the problem that an exoplanet inside the habitability zone of a red dwarf star has: tidal locking.
    In this scenario a gas giant may be tidal locked to the parent star but the exomoon is not. So the exomoon should have a better climate and may be suitable for life.
    A tellurian planet inside the habitability zone is always tidal locked and it is a bad handicap for life as we know it.
    Of course a red dwarf creates other problems: emission in infrared and terrible solar storms (solar flares) but this is another theme of discussion.
    I translated your great article to Portuguese and here is the link:

    Astrônomos começam a caça de exoluas orbitando exoplanetas
    http://eternosaprendizes.wordpress.com/2009/02/01/astronomos-comecam-a-caca-de-exoluas-orbitando-exoplanetas/
    So, let’s find the exomoons!
    Tks
    ROCA (Brazil)

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