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Data on 2 distant asteroids tease possibility of massive planet

Using the Gran Telescopio CANARIAS in Spain, for the first time, the dynamical properties of asteroids 2004 VN112 and 2013 RF98 were observed spectroscopically. The data suggest a possible common origin and gives a clue to the possible existence of a large planet deep in the Kuiper Belt. Image Credit: IAC

Observations of two extreme trans-Neptunian objects (ETNOs) suggest they were once part of a binary asteroid system that was perturbed by one or more undiscovered “super-Earth” planets that may still be lurking even further in the outer Solar System.

A team of researchers at the Instituto de Astrofisica de Canarias (IAC) and at Complutense University of Madrid, both in Spain, conducted spectroscopic observations of ETNOs 2004 VN112 and 2013 RF98, faint asteroids that orbit more than 150 astronomical units (AU) from the Sun. One AU is equal to the average Earth-Sun distance of about 93 million miles (150 million kilometers).

Approximately 21 ETNOs in similar orbits have been discovered since 2000. Because these objects’ orbits have similar dynamical parameters, several scientists recently proposed they are being perturbed by one or more massive planets orbiting the Sun as far as 700 AU.

Last year Mike Brown and Konstantin Batygin at Caltech predicted the existence of one super-Earth at around 700 AU based on the orbits of seven of the 21 known ETNOs.

CGI depiction of hypothetical 'Planet Nine' with lightning.

CGI depiction of hypothetical “Planet Nine” with lightning. Image Credit: Caltech / R. Hurt

The hypothesized outer Solar System planet is referred to by some scientists as Planet Nine and by others as Planet X. The latter is the conventional term used to refer to theorized but undiscovered objects.

Using the OSIRIS spectrograph on the Gran Telescopio CANARIAS (GTC), the research team, in cooperation with astronomers Gianluca Lombardi and Ricardo Scarpa, observed the two faint asteroids, successfully determined their apparent magnitudes, identified their compositions, and then refined the orbit of 2013 RF98.

Several striking similarities were found between the two objects. Their spectra – used to determine whether their surfaces have ices, silicates, and highly processed carbon compounds – were practically identical and very similar to those of two other ETNOs: 2000 CR105 and 2012 VP113.

“The similar spectral gradients observed for the pair 2004 VN112 [and] 2013 RF98 suggests a common physical origin”, said Julia de Leon, the lead author of a paper on the findings published in the Monthly Notices of the Royal Astronomical Society. “We are proposing the possibility that they were previously a binary asteroid which became unbound during an encounter with a more massive object”.

Sedna, the only other ETNO to have been spectroscopically observed, did not match the other four and is believed to have a different origin, having likely come from the inner Oort Cloud.

All five are among the seven ETNOs whose orbits led Brown and Batygin to hypothesize the existence of a distant, more massive planet.

To test the theory that these two objects were once partners in a binary asteroid system, the researchers conducted numerous computer simulations measuring how the poles of their orbits would separate once perturbation by a larger object pulled them apart.

The simulations supported the notion that a 10 to 20 Earth-mass planet orbiting between 300 and 600 AU from the Sun could have separated the two asteroids approximately five million to 10 million years ago.

A sequence of images taken with the Gran Telescopio Canarias to identify one of the ETNO´s studied, 2013 RF98. The left image shows how the asteroid moved during four consecutive nights. On the right is the visible spectra obtained with the GTC of the two objects, 2004 VN112 and 2013 RF98. The red lines show the gradients of the spectra. Image Credit: Julia de León / IAC



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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