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Asteroid at the Edge

Our current depictions of conditions in the early Solar System involve titanic change, with the giant planets moving inward and then outward, creating gravitational havoc and scattering inner system objects in all directions. Such disruptions doubtless happen in other infant planetary systems and because of them, we can predict a large population of so-called ‘rogue’ planets that move through the galaxy dissociated from any star. Closer to home, there may well be small objects kicked into extreme orbits that bear evidence of these migrations.

The ‘grand tack’ hypothesis sees Jupiter forming at around 3.5 AU, well in from its current 5.2 AU orbital position, with migration all the way in to 1.5 AU before a reversal of course and movement outward to its current position. Imagine Jupiter plowing through the asteroid belt — twice — and the chaos of its passage, producing a wide scattering in asteroid orbital inclinations and eccentricities. The ‘Nice model’ likewise involves gas giant migration, and has been invoked to explain the Late Heavy Bombardment as well as populations like the Kuiper Belt.

Now we learn of an observation that may teach us something about these events. A Kuiper Belt Object tagged 2004 EW95 is carbon-rich, typical of other carbonaceous asteroids in having a dark surface distinctive of carbon’s presence. This KBO, in other words, looks to be much like a main belt asteroid of the C-type, but it’s found at the edge of the system. The unusual spectral details turned up in work from Tom Seccull (Queen’s University Belfast) and colleagues, who used data from multiple instruments at the European Southern Observatory’s Very Large Telescope.

Image: The early days of our Solar System were a tempestuous time. Theoretical models of this period predict that after the gas giants formed they rampaged through the Solar System, ejecting small rocky bodies from the inner system to far-flung orbits at great distances from the Sun. Credit: ESO.

2004 EW95 had already been studied by Wesley Fraser, a member of Seccull’s team at Belfast, and it was in those observations, using the Hubble instrument, that it became clear that the object’s reflectance spectrum differed from the Kuiper Belt Objects around it. Whereas their spectra tend to be all but featureless, 2004 EW95 stood out. That merited a closer look through the VLT, producing an unusual observing challenge.

Imagine trying to study a dark object a mere 300 kilometers across as it moves through its orbit four billion kilometers from Earth. Co-author Thomas Puzia (Pontificia Universidad Católica de Chile) likens the task to observing a mountain of coal against a pitch black sky. The VLT’s X-Shooter spectrograph and FORS2 spectrograph and imager offered the precision needed. The paper calls the reflectance spectrum found here ‘unusual’ and states that it is:

…exhibiting a large drop in its near-UV reflectance and a broad shallow optical absorption feature centered at ∼700 nm, which is detected at greater than 4σ significance. These features, confirmed through multiple epochs of spectral photometry and spectroscopy, have respectively been associated with ferric oxides and phyllosilicates. The spectrum bears striking resemblance to those of some C-type asteroids, suggesting that 2004 EW95 may share a common origin with those objects.

The presence of ferric oxides and phyllosilicates marks 2004 EW95 as a kind of KBO that had never been found before, implying an origin far closer to the Sun. The phyllosilicate feature in the spectra, say the authors, points to significant heating in this object’s history, possibly radiogenic or the result of either solar irradiation or one or more collisions.

Each of these two features has been independently observed by two separate instruments, and are present in the reported reflectance spectra regardless of which of our solar calibrator targets, or which of two separate spectral extraction techniques, were used in our data reduction.

Thus 2004 EW95 takes us from a prediction made by two dynamical models of the early Solar System and fulfills that prediction in an actual KBO. The ‘grand tack’ model assumes that the early migrations of Jupiter and Saturn would have scattered carbonaceous asteroids that had formed near them and flung them into the outer Solar System, and we would thus expect that 2005 EW95 is not alone in the Kuiper Belt. From the paper:

The striking similarity between 2004 EW95 and certain C-type [carbonaceous] asteroids points to the plausible idea that 2004 EW95 shares a common origin with these objects. Taken together, the spectroscopic similarity to C-type asteroids and the orbital properties of 2004 EW95 are consistent with the idea that this object may have formed near Jupiter among the primordial C-type asteroids (Walsh et al. 2011) and was subsequently emplaced into the Kuiper Belt by the migrating planets.

So we have an object whose spectrum resembles those of primitive carbonaceous asteroids orbiting the Sun in a stable mean motion resonance with Neptune. Its orbit is highly inclined and eccentric, likely the result of dynamical instability and consistent with gas giant migration.

The paper is Seccull et al., ”2004 EW95: A Phyllosilicate-bearing Carbonaceous Asteroid in the Kuiper Belt,” Astrophysical Journal Letters 855, L26 (10 March 2018). Preprint / full text.

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{ 16 comments… add one }
  • Rob Flores May 9, 2018, 13:12

    Speaking of asteroids P. GILSTER,
    It would be useful to know how large an
    asteroid would be required for an impact that penetrates
    to the sub-surface oceans of Titan and Europa.

    Maybe a prof astronomer can tells us…
    Size required for each moon.
    Frequency of such impacts for each moon

    assuming there are no plate tectonics (of the Rocky cores),
    this is the only way biological building materials would be
    renewed on these moons.

    • Harry R Ray May 10, 2018, 10:27

      SPEAKING OF EUROPA: Marcia Smith tweeted this 17 hours ago. “Culbertson notes that $21.5b for NASA incl funding for Europa and hands out article to colegues that said was just published in “Nature Astronomy” saying Galileo flew through a Europa plume.”

      • ljk May 10, 2018, 16:50

        Why did it take 21 YEARS to report this event?! We have been talking and wondering about Europan plumes for years, especially their importance to finding life on that moon.

        https://gizmodo.com/congressman-divulges-unreleased-study-to-win-support-fo-1825915811

        • Harry R Ray May 11, 2018, 9:47

          A very simple reason for that! During that SPECIFIC flyby, they were NOT expecting a plume to be there in that SPECIFIC location, because no plumes had been detected prior to that flyby. Only AFTER the plume’s location was PINPOINTED a couple of years ago, could they THEN be able to go over OLD data taken when Galileo was OVER that specific location, to look for evidence of a plume! The same thing has just recently happened in a couple of instances with Voyager. In one instance, the FINAL aspects of Ganymede’s magnetic field were revealed in old voyager data, and in the other instance, by STACKING SEVERAL IMAGES TOGETHER of Enceladus, the plumes became visable, proving that Voyager, NOT Cassini, was the FIRST spacecraft to image them. Carolyn Porco just recently said that papers based on Cassini data will still be published FIFTY YEARS FROM NOW!!!

        • andy May 11, 2018, 14:30

          Good question. It’s definitely worth re-analysing the data from past missions. Apparently Voyager 1 may have observed the Enceladus plumes in 1980, but this wasn’t noticed at the time (I’m not sure the techniques used to process the image were available back then).

          • ljk May 11, 2018, 15:09

            In the July, 1981 issue of National Geographic Magazine that featured the results of Voyager 1’s flyby of Saturn in 1980, the article noted how bland the surface of Enceladus looked in images taken by the space probe, which only captured the moon from a fair distance. They speculated several ideas on why Enceladus seemed so smooth and shiny, including active geysers.

            This speculation included a two-page artwork spread showing the geysers, although they looked more like active cryovolcanoes. The point is the idea was put out there long before astronomers became aware of Enceladus’ geysers in 2005.

          • ljk May 11, 2018, 15:15

            Although I cannot remember precise dates here, there was an article (or at least a blurb/letter) in Sky & Telescope magazine circa 1982 about one of the Voyagers possibly imaging an active geyser on Europa during their 1979 flybys.

            The piece came complete with the image, which showed a fuzzy white patch on the moon. Some astronomer later said the probe had captured the dust cloud from a meteoroid impact, but I find the odds of that much harder to buy than a geyser detection, plus it just sounds like the person in question could not imagine Europa being active in that manner so came up with the meteor excuse.

            Anyone recall this or have a copy of the item itself to post here?

      • ljk May 11, 2018, 12:07

        May 11, 2018

        MEDIA ADVISORY M18-078

        NASA Hosts Live Discussion about Europa Findings, Potential for Life

        NASA will host a Science Chat at 1 p.m. EDT Monday, May 14, to discuss the latest analysis of Jupiter’s moon Europa and its status as one of the most promising places in the solar system to search for life.

        The event will air live on NASA Television, Facebook Live, Twitch TV, Ustream, YouTube, Twitter/Periscope and the agency’s website.

        https://www.nasa.gov/press-release/nasa-hosts-live-discussion-about-europa-findings-potential-for-life

  • Charley May 9, 2018, 15:33

    I’m getting the very, very distinct impression that the true “Goldilocks” life bearing regions that we will find in star systems will have a lot more to do with having a star with some type of ‘Jupiter like’ companion, rather than just a temperate zone for liquid water.
    It strikes me that ‘Jupiters’ have far greater impact in being able to sweep clean a lot of regions of asteroids then simply permitting aggregation of dust (if that’s what permits planet formation), then simply allowing dust clouds to coalesce into final planets.

    Simply permitting a large gravitator to dominate the planetary system does seem to do and awful lot of good in keeping the system clean of planetoids and asteroids which may threaten other smaller bodies.

    • ljk May 10, 2018, 9:30

      So what does this mean in terms of habitability for all those systems we have found where their Jupiters are so close to their stars?

      • Charley May 10, 2018, 15:25

        “Goldilocks” not ONLY just a temperate zone for liquid water

      • andy May 11, 2018, 14:35

        The formation models tend to predict that migration of giant planets into the inner system pulls a lot of icy material in with them. The expectation is that small planets formed exterior to giant planets will end up being extremely volatile-rich – i.e. ocean worlds and (sub-)Neptunes.

    • andy May 11, 2018, 14:49

      I definitely recall seeing papers that concluded that replacing Jupiter with a Saturn-mass planet is bad for HZ planets, as they are sufficiently massive to perturb material into the inner system but insufficiently effective at clearing material away. This is worse than either no Jupiter (lots of debris remains but not much gets to the inner system), or a Jupiter-analogue (most of the debris gets cleared out).

  • Alex Tolley May 9, 2018, 23:34

    The current models of the dynamic orbital history of celestial objects compared to the earlier, more static “clockwork” models reminds me of the paradigm shift when continental drift due to plate tectonics was accepted. This newer model may open up new explanations that would have been precluded by the older models.

  • DCM May 10, 2018, 16:22

    Another wandering interstellar asteroid drifting by?

  • ljk May 21, 2018, 11:45

    A New World’s Extraordinary Orbit Points to Planet Nine

    Astronomers argue that there’s an undiscovered giant planet far beyond the orbit of Neptune. A newly discovered rocky body has added evidence to the circumstantial case for it.

    In early 2016, two planetary scientists declared that a ghost planet is hiding in the depths of the solar system, well beyond the orbit of Pluto. Their claim, which they made based on the curious orbits of distant icy worlds, quickly sparked a race to find this so-called Planet Nine — a planet that is estimated to be about 10 times the mass of Earth.

    “It has a real magnetism to it,” said Gregory Laughlin, an astronomer at Yale University. “I mean, finding a 10-Earth-mass planet in our own solar system would be a discovery of unrivaled scientific magnitude.”

    Now, astronomers are reporting that they have spotted another distant world — perhaps as large as a dwarf planet — whose orbit is so odd that it is likely to have been shepherded by Planet Nine. The object confirms a specific prediction made by Konstantin Batygin and Michael Brown, the astronomers at the California Institute of Technology who first argued for Planet Nine’s existence.

    “It’s not proof that Planet Nine exists,” said David Gerdes, an astronomer at the University of Michigan and a co-author on the new paper. “But I would say the presence of an object like this in our solar system bolsters the case for Planet Nine.”

    Full article here:

    https://www.quantamagazine.org/a-new-worlds-extraordinary-orbit-points-to-planet-nine-20180515/

    To quote:

    Gerdes and his colleagues spotted the new object in data from the Dark Energy Survey, a project that probes the acceleration in the expansion of the universe by surveying a region well above the plane of the solar system. This makes it an unlikely tool for finding objects inside the solar system, since they mostly orbit within the plane. But that is exactly what makes the new object unique: Its orbit is tilted 54 degrees with respect to the plane of the solar system. It’s something Gerdes did not expect to see. Batygin and Brown, however, predicted it.

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