Back in the Solar System’s formative eons, a super-Earth may have accreted and swept up the material between present-day Mercury and the Sun, a new study suggests. Two scientists from the University of Nevada Las Vegas (UNLV) have theorized that not only a massive super-Earth exist in such close proximity of the Sun, but that said planet ultimately succumbed to the Sun’s enormous gravitational pull. That is correct: The Sun ate one of its planets.
Discovery News reported on April 14 that a new study published by UNLV astrophysicists Rebecca Martin and Mario Livio posits that at least one Super-Earth may be the responsible agent in clearing out a vast empty space inside the orbit of Mercury, an area completely bereft of orbiting material that has long puzzled scientists. The two authors believe that the evidence of such a hypothetical super-Earth clean-up in the Sun’s immediate neighborhood is the fact there is nothing — absolutely nothing — between Mercury and the Sun. And the modeling of their hypothesis supports their conclusion that after sweeping up all the space rocks near the Sun, the star eventually consumed the growing planet (or planets).
Rebecca Martin, lead author and a professor at UNLV, wrote as much to Discovery in an email:
“The only (physical) evidence that super-Earths could have formed in our solar system is the lack of anything in that region, not even a rock. So they could have formed there sweeping up all of the solid material, but then later fell into the sun.”
The authors based their hypothesis on observations made regarding other super-Earths discovered outside the Solar System. Martin and Livio found super-Earths usually formed in two places during the formation of planetary systems and that said formation was dependent upon density. Less dense super-Earths tended to form further out, away from the parent star. Denser super-Earths orbited much closer to their stars.
The authors suggest that one or more super-Earths formed in place and accreted the material inside of Mercury’s orbit. Temperature of the cooling protoplanetary disc — the primordial material that eventually, through accretion, divides and coalesces into the individual worlds and orbiting objects within a planetary system — would dictate the lifetime of the super-Earths. Martin and Livio posit that the overall temperatures would have been cool enough to see the large planets eaten by the Sun while the disc was still extant.
Admitting that confirmation studies would be necessary, Martin wrote the following.
“If the disc is sufficiently cool, the migration timescale for them to fall into the sun is short enough for this to happen in the lifetime of the disc.”
The UNLV astronomers aren’t the only scientists who have hypothesized that the Solar System was once home to super-Earths. According to a report by Science Magazine in March 2015, Jupiter may have also contributed to there being no overly large versions of the Earth orbiting the Sun.
In a paper that has bearing on work of the UNLV study, California Institute of Technology astronomer Konstantin Batygin and University of California Santa Cruz astronomer Gregory Laughlin formulated the “Grand Tack” theory after observing that there were super-Earths around more than half of the stars similar to our own that orbited in a roughly 100-day year around the parent stars. At the same time, only about 10 percent of those same systems contain planets as massive as Jupiter and Saturn.
The “Grand Tack” theory suggests that early in the Solar System’s formation, the massive planet actually migrated inward towards the Sun. But the later formation of massive Saturn acted as a giant gravity brake that would slow Jupiter and eventually pull it back away from the inner Solar System, where it would reach its current stable orbital path. As it moved inward and outward, Jupiter would have not only caused tumult and an untold number of collisions with its passage, it would have also collided with and consumed material, including planet-sized rocks. Some of those planets may have been super-Earth-sized worlds.
The “Grand Tack” theory was published in the Proceedings of the National Academy of Sciences. The Martin and Livio hypothesis about the protoplanetary super-Earths was published in the Astrophysical Journal. (preprint via arxiv.org).
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