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Helin, E. F.

Publications and source records attributed to Helin, E. F..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Recent discoveries and advances for the Near-Earth Asteroid Tracking program with MSSS 1.2-meter telescope

Jet Propulsion Laboratory's Near-Earth Asteroid Tracking (NEAT) program has two simultaneously-operating, autonomous search systems on two geographically-separated 1.2-m telescopes; one at the Maui Space Surveillance System (NEAT/MSSS) and the other on the Palomar Observatory's Oschin telescope (NEAT/Palomar). This paper will focus exclusively on the NEAT/MSSS system.

NEO near earth objects NEAT Near-Earth Asteroid Tr↗
NASA NTRS2002

An update of the Near-Earth Asteroid Tracking/Maui Space Surveillance System (NEAT/MSSS) collaboration

Jet Propulsion Laboratory's (JPL) Near-Earth Asteroid Tracking (NEAT) program has two simultaneously-operating, autonomous search systems on two geographically-separated 1.2-m telescopes; one at the Maui Space Surveillance System (NEAT/MSSS) and the other on the Palomar Observatory's Oschin telescope (NEAT/Palomar). This paper will focus exclusively on the NEAT/MSSS system.

NEAT MSSS↗
NASA NTRS1990

Search techniques for near-earth asteroids

Knowledge of the near-earth asteroids (Apollo, Amor, and Aten groups) has increased enormously over the last 10 to 15 years. This has been due in large part to the success of programs that have systematically searched for these objects. These programs have been motivated by the apparent relationships of the near-earth asteroids to terrestrial impact cratering, meteorites, and comets, and their relative accessibility for asteroid missions. Discovery of new near-earth asteroids is fundamental to all other studies, from theoretical modeling of their populations to the determination of their physical characteristics by various remote-sensing techniques. The methods that have been used to find these objects are reviewed, and ways in which the search for near-earth asteroids can be expanded are discussed.

Helin, E. F.↗
NASA NTRS1986

Sunward spike and equatorial plane of Halley's Comet

Photographs from late April until at least early June 1986 of comet Halley show a narrow spike in the Sun's direction. It extends to distances of at least 700,000 km from the nucleus in projection onto the sky on computer processed photographs. The spike is composed of dust and its enormous sunward extent (compared to other dust features) suggests an anomalously high ratio of particle ejection velocity to solar radiation pressure. The implied grains are either dielectric or slightly absorbing and much less than 1 micron in size, which are undetectable optically, unless Earth is located in or very near a plane of their concentration. The only plane to which these grains can possibly be confined for long is the equatorial plane of the nucleus, especially when the obliquity is small. Accordingly, the spike's position as a function of time contains information on the comet's spin axis.

Sekanina, Z.↗
NASA NTRS1986

Planet-Crossing Asteroid Search (PCAS)

511 independent fields were photographed with the 0.46m Schmidt during 15 observing runs along with a limited number of 1.2m Schmidt exposures. From these fields 122 new asteroids were reported. Special sets of field using the 1.2m Schmidt are continuing to yield numerous new faint asteroids. The combined result from both telescopes include 4 Mars-crossers, 3 Hungarias, 2 Phocaeas, a unique high inclination object (1985XB), 1 Apollo (1985PA) and Aten (3362) Khufu. Halley was regularly monitored (astrometry and large-scale phenomena) IHW participation. Scientifically value photographs were obtained from both 0.46m and 1.2m Schmidt Telescopes. Other accessible comets were observed including G-Z. Recently a new comet (1986d) was discovered.

Helin, E. F.↗
NASA NTRS1986

International collaboration leads to new Aten asteroid discovery, 1984 QA

A new earth-crossing asteroid of the Aten type (orbit smaller than earth's) was discovered on August 30, 1984 at Palomar. The asteroid, designated 1984 QA, is the fourth known member of the Aten type and the first discovered since 1978. The discovery of this object was the highlight of a collaboration between the JPL Asteroid Search Team and an ESA scientist, and demonstrates one aspect of an ongoing joint search effort with other Schmidt observers.

Helin, E. F.↗
NASA NTRS1985

Study and Estimation of Planet-crossing Asteroid Populations: Discoveries and Analysis

The populations of the various classes of planet-crossing asteroids, based on the results of the systematic Planet-Crossing Asteroid Survey (PCAS) search program are evaluated. Knowledge of the populations is crucial to the stimation of lunar and terrestrial planet cratering rates from asteroidal and cometary sources needed to establish the chronology of other surface features on those bodies. A secondary objective is to identify the sources of these crater-forming objects and their relative importance in producing the observed planet-crossing asteroid population. Some key PCAS asteroid discoveries relevant to the population problem and the progress in using the available search data to update and refine earlier estimates of the planet-crossing asteroid population are described.

Helin, E. F.↗
NASA NTRS1984

1984 AB - A unique Mars-crossing asteroid

Asteroid 1984 AB, discovered in January 1984, proved to be a unique object with a close dynamical relationship to Mars. A brief history of the discovery and subsequent 'evolution' of the orbit as it was refined is presented. The preliminary orbit of 1984 AB indicated that it might be a Mars Trojan, and an extended discussion of this interesting possibility is presented, but this hypothesis had to be dismissed after further observations had refined the orbit. The semimajor axis and orbital eccentricity are very similar to that of Mars. No other known Mars-crossing asteroid exists with an orbit as closely associated to Mars.

Helin, E. F.↗
NASA NTRS1984

The planet crossing asteroid survey: Progress in the analysis of populations and terrestrial-planet cratering rates

The Planet-Crossing Asteroid Survey (PCAS) is making steady progress toward the accumulation of the data required to make improved estimates of the populations and cratering rates which can be compared with the existing record of impact events. The PCAS is the chief source of new objects on which to base these calculations over the past decade, and is an integral part of the continuing refinement of the estimates used in planetological applications. An adjunct effort to determine albedo statistics from photometry of UCAS plates is being pursued as well, to better define the magnitude frequency distributions of asteroids. This will improve the quality of the population and collision probability calculations. The survey effort continues to discover new asteroids whose orbital characteristics may reveal the origin and evolution mechanisms reponsible for the transport of the planet-crossing asteroids to the inner solar system.

Helin, E. F.↗
NASA NTRS1984

The discovery of 1982 DB, the most accessible asteroid known

A small Apollo object was found while photographing the split comet DuToit 2-Hartley on February 27/28, 1982. Designated 1982 DB, this earth-crossing asteroid passed the earth at a distance of 4.08 million km about 1 month prior to its discovery. Asteroid 1982 DB has been determined to be the most accessible near-earth minor planet known. It provides many excellent opportunities for rendezvous and sample return missions, and a rare dual rendezvous mission with 1980 AA as the second target. For a mission to be realized, opportunities to observe 1982 DB during future apparitions must be taken.

Helin, E. F.↗
NASA NTRS1982

Earth-crossing asteroids - New discoveries

An earth-crossing asteroid is an asteroid whose orbit will intersect the orbit of the earth as a result of secular perturbations. Astronomical observations have led to the discovery of 43 earth-crossing asteroids during the last fifty years. Nearly sixty percent of these were found in the decade 1971-1981. Noteworthy results of the last decade are discussed, taking into account the Aten asteroids, accidental rediscoveries, asteroids of possible cometary origin, candidates for rendezvous and sample return missions, and populations and collision rates with earth. The observed earth-crossing asteroids are listed in a table, and the orbits of earth, Mars, and four Atens projected on ecliptic plane are shown.

Helin, E. F.↗
NASA NTRS1979

The Palomar planet-crossing asteroid survey, 1973-1978

Photographic coverage of about 80,000 sq deg of sky with the Palomar 46-cm Schmidt camera has yielded 12 new planet-crossing asteroids as well as many objects in the main asteroid belt. The estimated population of planet-crossing asteroids includes approximately 100 Atens, 700 + or- 300 Apollos, 1000-2000 Amors, 10,000 + or- 5000 Mars crossers, and approximately 5000 Mars grazers.

Helin, E. F.↗