Step On The Scales: Weighing Up Planet Earth…

Scientists at the European Southern Observatory have identified the closest looking solar system to our own. They located a sun-like star more than 100 light years distant with as many as seven different planets, including one that might be the smallest ever found outside the solar system.

“We have found what is most likely the system with the most planets yet discovered,” says Christophe Lovis, lead author of the paper reporting the result. “This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets. Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system.”

Some of the planets identified are large but one is only 1.4 times the size of Earth. That’s getting tantalizingly close to finding what astronomers are calling the ‘Holy Grail’ of astronomy, locating a planet just like our own with a breathable atmosphere, moderate temperatures and orbital stability. Scientists have been spotting planets beyond our solar system for the past 15 years, and they’ve now cataloged some 450. They know there are many more out there. The newly found worlds are made essentially of rocks and ice with a solid core. The larger planets probably have a layer of hydrogen and helium gas like Uranus and Neptune and the sixth is possibly a Saturn-like planet.

“We also have good reasons to believe that two other planets are present,” says Lovis. One would be a Saturn-like planet (with a minimum mass of 65 Earth masses) orbiting in 2200 days. The other would be the least massive exoplanet ever discovered [2], with a mass of about 1.4 times that of the Earth. It is very close to its host star, at just 2 percent of the Earth–Sun distance. One “year” on this planet would last only 1.18 Earth-days.

“This object causes a wobble of its star of only about 3 km/hour — slower than walking speed — and this motion is very hard to measure,” says team member Damien Ségransan. If confirmed, this object would be another example of a hot rocky planet, similar to Corot-7b.

Since the Earth is suspended in space, it cannot be put on a scale and weighed to be compared to other planets. But scientists can estimate its total weight by, among other things, measuring its tug on orbiting satellites. We’ve used this method to weigh the Earth and it turns out to be a whopping 6.6 sextillion tons… that’s two 6s, followed by twenty zeros, or 6,600,000,000,000,000,000,000 tons! But Earth’s weight gain doesn’t stop there… it increases by 100,000 pounds each year from dust and meteoric material falling from the sky. How does this “weigh up” to planetary science?

“Clearly, the exploration of the low-mass planet population has now fully started,” says C. Lovis et al. “The HARPS search for southern extra-solar planets will become the main focus of the field in the coming years. It is expected that the characterization of planetary system architectures, taking into account all objects from gas giants to Earth-like planets, will greatly improve our understanding of their formation and evolution. It will also allow us to eventually put our Solar System into a broader context and determine how typical it is in the vastly diverse world of planetary systems. The characterization of a significant sample of low-mass objects, through their mean density and some basic atmospheric properties, is also at hand and will bring much desired insights into their composition and the physical processes at play during planet formation.”

Many thanks to Dave Reneke of Australasian Science Magazine for sharing and to Mission Green Globe and ESO for the images.

15 Replies to “Step On The Scales: Weighing Up Planet Earth…”

  1. Scientists at the European Southern Observatory have identified the closest looking solar system to our own.

    Why does everyone insist on calling this system “closest looking” to our own? Did our gas giants suddenly decide to start orbiting closer to the sun then Mercury? Please make me understand this reasoning. This system looks very alien to our own to me.

  2. All well and good, but I would be satisfied with terrestrials that are 2 Earth radius or less. The essentially same gravity would give climate, seas and life like ours. (Well, their largest land animals would be smaller.)

    it increases by 100,000 pounds each year from dust and meteoric material

    Too bad that material doesn’t make up for atmospheric losses.

    Which makes me wonder under what circumstances a dust/meteor influx would eventually reverse atmospheric losses. (As the planetary mass grows, while some of that influx is volatiles.) Fun coffee table problem!

    Nitpick: Pounds isn’t an SI unit, which is bad in itself in this here type of blog. But it is even more so when compared against metric tons in the previous sentence. (And FWIW, ton is, or at least used to be, an SI supplementary unit.)

  3. [Note to admin: the page script is broken. I did _not_ format the previous comment as italics.]

    @ Uncle Fred:

    To give the context to your question, I prefer to see how the new observations filled in gaps in our understanding of planetary systems. Because from earlier data and not yet fully released Kepler data, we know that our solar system is rather typical:

    – Stars with lower and higher mass have planets.
    – Stars with lower and higher metallicity have planets. (In fact, the Sun is precisely on the broad plateau of number of planets.)
    – Our planets masses makes a pattern that matches exactly the exoplanet mass distribution. (This is from a semi-famous TED talk of early Kepler data.) I.e. we would expect 4 planets with masses smaller than 2 Earth masses, 2 planets in the next bin with masses up to Neptune, 1 Saturn-like, 1 Jupiter like, and none larger.
    – There are smaller and larger radius planetary systems.
    – Our system follows the packing rule that others seem to follow: you can’t put a planet between existing planets and not getting it (smaller planet) or one of the others (larger planet) thrown out.
    – Other systems have been seen with analogs to asteroid belts and Kuiper belts, and comets crashing into their suns (presumably an Oort belt comet reservoir beside the Kuiper one).

    In this context the new system answered the remaining question of Sun typicalness: there are (seem to be) planet systems with as many planets as ours. That is good news!

    As for the remaining part of your question, what else is typical with the new system, i.e. how much does it resemble ours, I’ll take from memory, but I think:
    – roughly the same mass-number pattern of planets.
    – roughly the same terrestrials inner, giants outer pattern as ours.
    – roughly the same size (within a factor of two or so).
    – an asteroid belt.
    – follows the packing rule. IIRC, the ESO paper gets into that a lot, as they think they can extract something reminding of Titius-Bode law from it and have started to look for data testing that.

    So our system and the new one is rather typical in many respects, and remind of each other in the remaining. (Specifically the inner-outer pattern, IIRC.) If it is the “closest looking”, however, is a question that either would need a very complicated metric to answer, or an expert.

  4. @ Uncle Fred:

    Oops, prompted by another post I see that I forgot planetary eccentricity.

    Our planets seem to be within the typical range there too, albeit I dunno if such a low total summed eccentricity have been seen. The new system didn’t do too bad there, IIRC.

  5. ahhh okay. Thanks a bunch OM. This explanation makes more sense.

    This is all very encouraging news. I await the full release of the Keplar data with batted breath.

    Sorry to get a little off topic however I do have a second question to pose. I’m still a little curious about what exactly the Kepler team are releasing. Is it only the data taken from the first 40 something days of study?

    I imagine we’d have to wait the full three years before they could confirm any terrestrial sized planets orbiting at 1 AU. Do you guys know/think that they’ll release data more quickly? What is the earliest likelyhood of detecting a Earth sized planet in the goldilocks zone of a G type Mainsequence star?

    I feel so inexperienced asking these questions but I figured some of you guys have a better grasp on this research. Maybe I’m just getting excited over the speed these findings are coming in.

  6. Wow. The opening line says it all. “Scientists at the European Southern Observatory…” and yet we are shown in the welcoming graphic, with open hands mind you, with an Earth image with North America central to the frame.

    Eh. No. Europe is in the same hemisphere, but is a bit ti the right. The observatory itself is in the southern hemisphere, south of the position of the image.

    America, as far as I know, is not the centre of astronomy in this world nor is among the senior partner in the ESO.

    We know Dave Reneke did go missing for a while in Australia, though I now suspect he might slid in and either become a US citizen or has been indoctrinated by one of its security agencies or the “Mission Green Globe.”

    (Who the hell is “Mission Green Globe” anyway? I could find not links to it except some globe trotting company in San Juan, Puerto Rico! Ah! Probably part of the North American plan or plot for world domination? Figures)

  7. The appearance of N. America is immaterial. The most famous image of the Earth is the one which features Africa prominently, and Africa is not a major region of scientific activity.

    This stellar system is similar to ours, but has enough departures to make it probably less optimal for a planet similar to Earth. The 5 inner planets might gravitationally perturb a terrestrial planet too much to make it favorable for life. What is being found is there is a huge variety of stellar systems which exist, and so it may turn out that our solar system is not entirely exceptional, or no more exceptional than many other configurations.

    LC

  8. Since reading this, and doing a little search on the web, I think you might find that you “earth and hands” image might be just breaking copyright on someone else’s company logo. Since I’m not sure, I sent them a little email to confirm the origin of this image.
    “Uncle Dave” probably should be asked where he got the image from. It might be prudent.

  9. @ Lawrence

    Correct. “The appearance of N. America is immaterial.” However, it is brazenly subliminal and deliberately provokes the usual American imperialistic centralism we have come to expect.

    As for “Africa is not a major region of scientific activity.” Eh? Africa is not Europe!! Clearly the ESO is far from a minor player in science.

  10. “He’s got the whole wide world, in his hands!” This image takes me back to Sunday School! LOL! Patent THAT! dzzzzz…..

  11. Uncle Fred, LBC comment makes me suspect that I messed up some of the “like points”. (I have a nasty cold, so are literary commenting in fever – fun things happen.) You may have to check that out, sorry about that.

    You are correct on the early Kepler data. It was something like ~ 700 signals IIRC, half of which were expected to turn up as planets (and not coincident solar spots et cetera).

    These early data was used for extrapolation at larger distances, say on the mass/number distribution. We will still have to wait nearly 3 years before they release candidate signals, 2-3 orbits, for habitable zone (HZ) Earth analogs around Sun analogs. (But not as long at all for red dwarfs, which have much smaller HZ’s.)

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