Julia de León

The Origin of Asteroid 101955 (1999 RQ36)

Near-Earth asteroid (NEA) 101955 (1999 RQ36; henceforth RQ36) is especially accessible to spacecraft and is the primary target of NASAs OSIRIS-REx sample return mission; it is also a potentially hazardous asteroid. We combine dynamical and spectral information to identify the most likely main-belt origin of RQ36 and we conclude that it is the Polana family, located at a semimajor axis of about 2.42 AU. We also conclude that the Polana family may be the most important inner-belt source of low-albedo NEAs. These conclusions are based on the following results. (1) Dynamical evidence strongly favors an inner-belt, low-inclination (2.15 AU < a < 2.5 AU and i < 10°) origin, suggesting the ν6 resonance as the preferred (95% probability) delivery route. (2) This region is dominated by the Nysa and Polana families. (3) The Polana family is characterized by low albedos and B-class spectra or colors, the same albedo and spectral class as RQ36. (4) The Sloan Digital Sky Survey colors show that the Polana family is the branch of the Nysa-Polana complex that extends toward the ν6 resonance; furthermore, the Polana family has delivered objects of the size of RQ36 and larger into the ν6 resonance. (5) A quantitative comparison of visible and near-infrared spectra does not yield a unique match for RQ36; however, it is consistent with a compositional link between RQ36 and the Polana family.

THE ORIGIN OF ASTEROID 162173 (1999 JU3)

Near-Earth asteroid (162173) 1999 JU3 (henceforth JU3) is a potentially hazardous asteroid and the target of the Japanese Aerospace Exploration Agencys Hayabusa-2 sample return mission. JU3 is also a backup target for two other sample return missions: NASAs OSIRIS-REx and the European Space Agencys Marco Polo-R. We use dynamical information to identify an inner-belt, low-inclination origin through the ν6 resonance, more specifically, the region with 2.15 AU < a < 2.5 AU and i < 8°. The geometric albedo of JU3 is 0.07 ± 0.01, and this inner-belt region contains four well-defined low-albedo asteroid families (Clarissa, Erigone, Polana, and Sulamitis), plus a recently identified background population of low-albedo asteroids outside these families. Only two of these five groups, the background and the Polana family, deliver JU3-sized asteroids to the ν6 resonance, and the background delivers significantly more JU3-sized asteroids. The available spectral evidence is also diagnostic; the visible and near-infrared spectra of JU3 indicate it is a C-type asteroid, which is compatible with members of the background, but not with the Polana family because it contains primarily B-type asteroids. Hence, this background population of low-albedo asteroids is the most likely source of JU3.

Nuclear Spectra of Comet 162P/Siding Spring (2004 TU12)

We present visible and near-IR spectra of the nucleus of comet 162P/Siding Spring (also known as 2004 TU12) obtained in 2004 December, while it had no detectable coma. This is the third object observed to have intermittent cometary activity even when relatively close to the Sun. The spectra show no strong features in this wavelength range. This paucity of deep absorptions is common among low-albedo asteroids and the few comet nuclei observed in this spectral region. Marginal spectral structure is observed in the visible spectrum, and beyond 2 μm the flux from the nucleus is dominated by thermal emission. We compare the spectrum of 162P with published spectra of other comet nuclei, primitive asteroids, and meteorites. Comet nuclei display a range of spectral shapes and slopes not unlike those observed among outer main-belt asteroids but closest to Trojan asteroids. No suitable spectral matches to comet 162P were found among primitive (chondritic) meteorites. We modeled our visible and near-IR spectra using the scattering theory described by Shkuratov et al. (1999), and our approach is similar to that used by Emery and Brown for modeling Trojan asteroids. Our best fits to the spectral shape and albedo include mixtures containing amorphous carbons, organics, and silicates. The absence of strong spectral features prevents the identification of specific minerals, and the resulting model compositions are not unique. The observations beyond 2 μm are interpreted in a companion publication by Fernandez and coworkers.

Compositional study of asteroids in the Erigone collisional family using visible spectroscopy at the 10.4 m GTC

Two primitive near Earth asteroids, (101955) Bennu and (162173) Ryugu, will be visited by a spacecraft with the aim of returning samples back to Earth. Since these objects are believed to originate in the inner main belt primitive collisional families (Erigone, Polana, Clarissa, and Sulamitis) or in the background of asteroids outside these families, the characterization of these primitive populations will enhance the scientific return of the missions. The main goal of this work is to shed light on the composition of the Erigone collisional family by means of visible spectroscopy. Asteroid (163) Erigone has been classified as a primitive object, and we expect the members of this family to be consistent with the spectral type of the parent body. We have obtained visible spectra (0.5 to 0.9 microns) for 101 members of the Erigone family, using the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias. We found that 87 percent of the objects have typically primitive visible spectra consistent with that of (163) Erigone. In addition, we found that a significant fraction of these objects (approximately 50 percent) present evidence of aqueous alteration.

Nuclear Spectra of Comet 28P Neujmin 1

We present visible and near-infrared spectra of the nucleus of comet 28P/Neujmin 1, obtained in 2001, 2002, and 2003, while it had no detectable coma. The spectra show no strong features in this wavelength range, which prevented the identification of specific compounds on the surface of comet 28P. We found evidence for spectral variability, as our 2002 near-infrared spectrum has a significantly steeper slope than those obtained in 2001 and 2003. We compare the spectra of 28P with published spectra of other comet nuclei, with primitive asteroids and with meteorites. At near-infrared wavelengths, all the comet nuclei show spectra with red slopes and the 2002 spectrum of comet 28P is among the reddest even when compared with Trojan asteroids. Three of the four properly observed Jupiter-family comets have significantly redder spectral slopes in the near-infrared than the one Halley-type comet in this sample. We found reasonably good matches among Trojan asteroids to the albedo and spectral shape of comet 28P. Such similarities are consistent with an analogous formation and evolutionary environment for Trojan asteroids and Jupiter-family comets, as proposed by Morbidelli and coworkers. One CI meteorite showed a partial fit to our 2003 near-infrared spectrum of comet 28P; however, no close spectral matches to our target were found among chondritic meteorites.

Visible spectroscopy of the Sulamitis and Clarissa primitive families: a possible link to Erigone and Polana

The low-inclination ( i ∘ ) primitive asteroid families in the inner main belt, that is, Polana-Eulalia, Erigone, Sulamitis, and Clarissa, are considered to be the most likely sources of near-Earth asteroids (101955) Bennu and (162173) Ryugu. These two primitive NEAs will be visited by NASA OSIRIS-REx and JAXA Hayabusa 2 missions, respectively, with the aim of collecting samples of material from their surfaces and returning them back to Earth. In this context, the PRIMitive Asteroid Spectroscopic Survey (PRIMASS) was born, with the main aim to characterize the possible origins of these NEAs and constrain their dynamical evolution. As part of the PRIMASS survey we have already studied the Polana and Erigone collisional families in previously published works. The main goal of the work presented here is to compositionally characterize the Sulamitis and Clarissa families using visible spectroscopy. We have observed 97 asteroids (64 from Sulamitis and 33 from Clarissa) with the OSIRIS instrument (0.5-0.9 μ m) at the 10.4 m Gran Telescopio Canarias (GTC). We found that about 60% of the sampled asteroids from the Sulamitis family show signs of aqueous alteration on their surfaces. We also found that the majority of the Clarissa members present no signs of hydration. The results obtained here show similarities between Sulamitis-Erigone and Clarissa-Polana collisional families.