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Tholen, David J.

Publications and source records attributed to Tholen, David J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus

We are conducting a survey using twilight time on the Dark Energy Camera with the Blanco 4 m telescope in Chile to look for objects interior to Earth's and Venus' orbits. To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo-type Near Earth Object (NEO) that crosses Earth's orbit, 2022 AP7. Two of the discoveries have diameters ≳1 km. 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years. To date we have covered 624 square degrees of sky near to and interior to the orbit of Venus. The average images go to 21.3 mag in the r band, with the best images near 22nd mag. Our new discovery 2021 PH27 has the smallest semimajor axis known for an asteroid, 0.4617 au, and the largest general relativistic effects (53 arcsec/century) known for any body in the solar system. The survey has detected ~15% of all known Atira NEOs. We put strong constraints on any stable population of Venus co-orbital resonance objects existing, as well as the Atira and Vatira asteroid classes. These interior asteroid populations are important to complete the census of asteroids near Earth, including some of the most likely Earth impactors that cannot easily be discovered in other surveys. Comparing the actual population of asteroids found interior to Earth and Venus with those predicted to exist by extrapolating from the known population exterior to Earth is important to better understand the origin, composition, and structure of the NEO population.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Physical Characterization of Interstellar Comet 2I/2019 Q4 (Borisov)

We present a study of interstellar comet 2I/2019 Q4 (Borisov) using both preperihelion and postperihelion observations spanning late September 2019 through late January 2020. The intrinsic brightness of the comet was observed to continuously decline throughout the timespan, likely due to the decreasing effective scattering cross-section as a result of volatile sublimation with a slope of −0.43 ± 0.02 km{sup 2} d{sup −1}. We witnessed no significant change in the slightly reddish color of the comet, with mean values of 〈g−r〉=0.68±0.04, 〈r−i〉=0.23±0.03, and the normalized reflectivity gradient across the g and i bands (S{sup ′})-bar (g,i)=(10.6±1.4)% per 10{sup 3} Å, all unremarkable in the context of solar system comets. Using the available astrometric observations, we confidently detect the nongravitational acceleration of the comet following a shallow heliocentric distance dependence of r{sub H}{sup −1±1}. Accordingly, we estimate that the nucleus is most likely ≲0.4 km in radius, and that a fraction of ≳0.2% of the total mass of the nucleus has been eroded due to the sublimation activity since the earliest observation of the comet in 2018 December by the time of perihelion. Our morphology simulation suggests that the dust ejection speed increased from ∼4 m s{sup −1} in 2019 September to ∼7 m s{sup −1} around perihelion for the optically dominant dust grains with β∼0.01, and that the observable dust grains are no smaller than micron size.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

A New High Perihelion Trans-Plutonian Inner Oort Cloud Object: 2015 TG387

Inner Oort cloud objects (IOCs) are trans-Plutonian for their entire orbits. They are beyond the strong gravitational influences of the known planets, yet close enough to the Sun that outside forces are minimal. Here we report the discovery of the third known IOC after Sedna and 2012 VP113, called 2015 TG387. This object has a perihelion of 65 ± 1 au and semimajor axis of 1170 ± 70 au. The longitude of perihelion angle, ω-bar , for 2015 TG387 is between that of Sedna and 2012 VP113 and thus similar to the main group of clustered extreme trans-Neptunian objects (ETNOs), which may be shepherded into similar orbital angles by an unknown massive distant planet called Planet X, or Planet Nine. The orbit of 2015 TG387 is stable over the age of the solar system from the known planets and Galactic tide. When including outside stellar encounters over 4 Gyr, 2015 TG387's orbit is usually stable, but its dynamical evolution depends on the stellar encounter scenarios used. Surprisingly, when including a massive Planet X beyond a few hundred au on an eccentric orbit that is antialigned in longitude of perihelion with most of the known ETNOs, we find that 2015 TG387 is typically stable for Planet X orbits that render the other ETNOs stable as well. Notably, 2015 TG387's argument of perihelion is constrained, and its longitude of perihelion librates about 180° from Planet X’s longitude of perihelion, keeping 2015 TG387 antialigned with Planet X over the age of the solar system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

RADIATION PRESSURE DETECTION AND DENSITY ESTIMATE FOR 2011 MD

We present our astrometric observations of the small near-Earth object 2011 MD (H ∼ 28.0), obtained after its very close fly-by to Earth in 2011 June. Our set of observations extends the observational arc to 73 days, and, together with the published astrometry obtained around the Earth fly-by, allows a direct detection of the effect of radiation pressure on the object, with a confidence of 5σ. The detection can be used to put constraints on the density of the object, pointing to either an unexpectedly low value of ρ=(640±330)kg m{sup −3} (68% confidence interval) if we assume a typical probability distribution for the unknown albedo, or to an unusually high reflectivity of its surface. This result may have important implications both in terms of impact hazard from small objects and in light of a possible retrieval of this target.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2004

Observations of the Pluto-Charon System

We are continuing the analysis of adaptive optics observations of the Pluto-Charon system, with the goal of confirming the orbital eccentricity reported by Tholen and Bule (1997). Previous work on these data, obtained with the Hokupa's adaptive optics system and Gemini North and reported by Tholea (2002), utilized only a portion of the full set of 348 images taken on 8 nights between 2001 and 2002, and was based on a preliminary calibration of the image scale and position angle of the detector. For each of the three observing runs, independent calibrations were performed using the motion of an asteroid past a fixed stellar source to remove any minor differences in the way the instrument was mounted on the telescope for each run. The image scales determined for each run are good to better than 1 part in 1000, while the individual position angle determinations are good at least 0.1 deg. The preliminary analysis reported at last year's DPS meeting indicated consistency with the orbit determined from the HST observations acquired a decade ago, however, a more careful analysis yields a longitude of periapsis of 132.2 degrees plus or minus 9.3 degrees, disagreeing with the HST results: Finally, possible explanation for the differences in orbital solutions are considered.

Tholen, David J.↗
NASA NTRS2003

Search for Near-Earth Objects with Small Aphelion Distances

An essential component of our ability to efficiently find NEOs at small solar elongation is a focal reducer, whose construction is being separately funded by a grant from NSF. This focal reducer will increase the field of view of the 8k CCD mosaic camera from 19 arc min to about 32 arc min at the Cassegrain focus of the University of Hawaii 2.24-m telescope. As of January, all but one of the lenses for the focal reducer were in hand. The final lens had been delayed due to problems with the availability of the rather exotic material out of which the manufacturer was to fabricate the lens. Perhaps as a result of their rush to deliver that final lens, it developed a crack during the annealing process at the manufacturer, thus they had to start over. The total delay in delivery of that last lens was nearly ten months, and therefore the focal reducer was not completed on schedule and could not be used on the telescope this semester. A postdoctoral research associate was recruited to handle the day-to-day operations. The closing date for applications was 2002 December 3 1, and seven were received. One applicant was not qualified, and two were marginal. Of the four qualified candidates, Fabrizio Bernardi stood out as being best qualified. He was a student of Andrea Carusi and had worked on the CINEOS project in Italy, which includes a component of searching for NEOs at small solar elongations.

Tholen, David J.↗
NASA NTRS2002

Observations of Planet Crossing Asteroids

The goals of this research were the physical and dynamical characterization of planet crossing asteroids (Earth crossers, Mars crossers, Centaurs, and Pluto crossers, meaning trans-Neptunian objects), including colorimetry, rotational studies, and astrometry. Highlights are listed as follows: 1) Produced one doctoral dissertation (R. J. Whiteley, A Compositional and Dynamical Survey of the Near-Earth Asteroids). A key result is the fraction of Q-type asteroids among the near-Earth population was found to be about one-third; 2) Had prediscovery image showing the binary nature of trans-Neptunian object 1998 WW31, which is the first TNO to have a satellite found in orbit around it; 3) Discovery of shortest known rotation period for any asteroid (2000 D08, rotation period 78 seconds); it is just one of several fast-rotating small asteroids observed during the course of this project; 4) Discovery of a Centaur asteroid (1998 QM107) with, at the time, the smallest known orbital eccentricity among the Centaurs (0.13) and nearly in a 1:1 resonance with Uranus (semimajor axis of 19.9 AU); 5) Discovery of Apollo-type asteroid 1999 OW3, with a surprisingly bright absolute magnitude of 14.6 (estimated diameter of 4.6 km), brightest Apollo found in that calendar year; 6) Discovery of Aten-type asteroid 2000 SG344, which has the highest cumulative Earth impact probability among the near-Earth asteroids and a very Earth-similar orbit; 7) Instrumental in repairing the orbit of a numbered near-Earth asteroid for which prediscovery observations had been mis-attributed to it (2000 VN2); 8) Second-opposition recovery of 30-meter diameter Apollo-type asteroid 1998 KY26 in early 2002 when it was at a favorable magnitude of 24.8; 9) Primary contributor of astrometric observations of the CONTOUR fragments to the CONTOUR project following the failure of the spacecraft s kick motor; and 10) Development of orbit and ephemeris computation code that handles short observational arcs, observations at small solar elongations where indeterminacy is a known problem, and a small number of observations (including just two). Starting in 2000 November, the Spaceguard Central Node began prioritizing near-Earth asteroids in need of astrometric observation. Our own follow-up efforts relied on these listings, with emphasis given to the faintest objects where the combination of a 2.2-m telescope and a site with subarcsecond seeing produces a limiting magnitude close to 25, which represents a unique and valuable capability. The attached table, last updated in August, demonstrates the arc-lengthening capabilities of a faint limiting magnitude. Tabulated are the arc lengths before and after our observation(s), whether our observation is the last one available for the object in question, and the approximate magnitude of the object at the time of the observation.

Tholen, David J.↗
NASA NTRS2001

Observation and Analysis of Jovian and Saturnian Satellite Mutual Events

The main goal of this research was to acquire high time resolution photometry of satellite-satellite mutual events during the equatorial plane crossing for Saturn in 1995 and Jupiter in 1997. The data would be used to improve the orbits of the Saturnian satellites to support Cassini mission requirements, and also to monitor the secular acceleration of Io's orbit to compare with heat flow measurements.

Tholen, David J.↗
NASA NTRS1999

Observations of Planet Crossing Asteroids

This grant funds the investigation of the Solar System's planet crossing asteroid population, principally the near Earth and trans-Neptunian objects, but also the Centaurs. Investigations include colorimetry at both visible and near infrared wavelengths, light curve photometry, astrometry, and a pilot project to find near Earth objects with small aphelion distances, which requires observations at small solar elongations.

Tholen, David J.↗
NASA NTRS1998

Observations of Spacecraft Targets, Unusual Asteroids, and Targets of Opportunity

Obtain physical and astrometric observations of: (1) spacecraft targets to support mission operations; (2) known asteroids with unusual orbits to help determine their origin; and (3) newly discovered minor planets (including both asteroids and comets) that represent a particular opportunity to add significant new knowledge of the Solar System.

Tholen, David J.↗
NASA NTRS1994

Pluto's lightcurve: Results from four oppositions

The rotational lightcurve, phase function, and orbital lightcurve of the Pluto-Charon system were measured in blue light over four consecutive oppositions spanning 1980 to 1983. Compared with observations made in the three previous decades, our lightcurve shows a higher amplitude of 0.29 mag, as well as a fainter rotationally averaged brightness, which provide constraints on the surface albedo distribution of the two bodies. The synodic rotational period of 6.38726 +/- 0.00007 days is consistent with the orbital period of Charon, which provides evidence for a completely tidally evolved system. The phase coefficient is 0.0372 +/- 0.0016 mag/deg, indicating a very shallow opposition surge compared with asteroids, but consistent with a high albedo surface. The orbital lightcurve shows substantially less fading than the earlier observations, which suggests that there is not a gross difference in average albedo between the southern and northern hemispheres.

Tholen, David J.↗
NASA NTRS1992

Comparison of asteroid and meteorite spectra - Classification by principal component analysis

The spectra of 103 meteorites and 411 asteroids have been statistically compared via principal component analysis, in order to arrive at an overview of spectral similarities between and among asteroids and meteorites; the result is a map of statistically defined relative spectral similarities measured by distance. There is much more spectral variance in the meteorites than in the asteroids. The analysis indicates no direct meteorite analogs from the outer-belt B, D, F, P, and T type asteroids, indicating that only a limited portion of the inner asteroid belt is sampled by meteorites.

Britt, Daniel T.↗
NASA NTRS1992

Albedo maps of Pluto and Charon - Initial mutual event results

By applying the technique of maximum entropy image reconstruction to invert observed lightcurves, surface maps of single-scattering albedo are obtained for the surfaces of Pluto and Charon from 1954 to 1986. The albedo features of the surface of Pluto are similar to those of the Buie and Tholen (1989) spot model maps; a south polar cap is evident. The map of Charon is somewhat darker, with single-scattering albedos as low as 0.03.

Buie, Marc W.↗
NASA NTRS1992

Extraordinary colors of asteroidal object (5145) 1992 AD

The colors of the recently discovered 1992 AD indicate a heretofore unknown spectral class, with colors that are far redder than those of any asteroids and comets thus far studied. It is suggested that the redness may be due to the exposure of organic substances that are purer than those associated with C, P, and D asteroids and comets, and therefore more likely to exhibit diagnostic spectral features in the IR.

Mueller, Beatrice E. A.↗
NASA NTRS1991

Visible and infrared investigations of planet-crossing asteroids and outer solar system objects

A major effort was directed toward 951 Gaspra in preparation for the Galileo encounter in October 1991. Most of the observational work involved photometry, for purposes of investigating the rotational state and phase function of the asteroid to help plan the encounter, and for purposes of navigating the spacecraft to the object. Work was also done with radiometric data obtained with the IRTF at NASA's request, for which simultaneous visible photometry was acquired with the University of Hawaii 2.24-m telescope. The results from the observations made during the 1990 opposition were published by Goldader et al. The main results reported include a rotational period of 7.04246 hours, an absolute visual magnitude of 11.8026, a slope parameter of 0.285, an early estimate of a high obliquity, an infrared spectrum indicating an olivine-rich composition, and 13 astrometric positions.

Tholen, David J.↗
NASA NTRS1991

Galileo support observations of Asteroid 951 Gaspra

Observations of 951 Gaspra in support of the Galileo spacecraft encounter are reported. Photometric observations of the asteroid yield a synodic rotational period of 7.042 46 and a slope parameter G of 0.285 + or - 0.005. It is inferred from data obtained on May 18, 1990, that the subearth latitude was higher at that time than it was earlier in the opposition. This places a limit on the possible pole orientation of the asteroid. A slope parameter of 0.25 is proposed on the basis of a comparison of the present result for the slope parameter with that of Barucci et al. (1990). A low-quality 0.8-2.5-micron spectrum of 951 Gaspra suggests a high olivine/pyroxene ratio, which is indicative of a source region in the lower mantle of a differentiated asteroid, and similarities to 8 Flora and particularly 15 Eunomia.

Goldader, Jeffrey D.↗
NASA NTRS1991

Studies of Triton and the Pluto-Charon system

The project is designed to take advantage of the six-year-long series of mutual occultation and eclipse events involving Pluto and its satellite Charon during one of its rare edge-on orbital alignments. High-precision, high-time-resolution photometry of these events can be utilized to extract several important physical parameters. An important derived parameter is the mean density of the system, which constrains the bulk composition of two bodies.

Tholen, David J.↗