A review of comet and asteroid statistics

Gehrels, T.

doi:10.1186/bf03351590

Cited by 5 publications

(3 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However this is a recent event. Compare with what Tom Gehrels (1999) has to say about former asteroidal photometry (equally valid for cometary photometry): "Before the 50s, asteroid magnitudes were not usable for statistics. They would be off by as much as 3 magnitudes: fainter than the 11th magnitude, they tended to be all the same because the Bonner Durchmusterung had been used for calibration an it did not go fainter."…”

Section: Mean Phase Coefficient For Cometsmentioning

confidence: 87%

Secular light curve of Comet 28P/Neujmin 1 and of spacecraft target Comets 1P/Halley, 9P/Tempel 1, 19P/Borrelly, 21P/Giacobinni–Zinner, 26P/Grigg–Skjellerup, 67P/Churyumov–Gerasimenko, and 81P/Wild 2

Ferrin¹

2007

Icarus

View full text Add to dashboard Cite

We present the secular light curves of eight comets listed in the title. Two plots per comet are needed to study these objects: a reduced magnitude (to = 1 AU = geocentric distance) vs time, and a reduced magnitude vs Log R (R = heliocentric distance). A total of over 16 new parameters, are measured from both plots, and give an unprecedented amount of information to characterize these objects: the onset of sublimation (R ON ), the offset of sublimation (R OFF ), the time lag at perihelion (LAG), the absolute magnitude (m(1, 1)), the maximum magnitude at perihelion (m MAX (1, LAG)), the nuclear magnitudes (V N ), the amplitude of the secular light curve (A SEC ), plus several others, and the photometric functions needed to describe the envelope. The most significant findings of this investigation are: (a) The envelope of the observations is the best representation of the secular light curve. (b) The H10 photometric system is unable to explain the curves and a new set of photometric rules and functions is used. (c) Only four comets exhibit power laws in their secular light curves, and only partially: 1P, 19P, 21P, and 81P. All others have to be described by more complex functions. Of the four, three exhibit a break of the power law, requiring two laws pre-perihelion and one post-perihelion. The reason for this behavior is not understood. (d) We predict the existence of a photometric anomaly in the secular light curve of 67P/Churyumov-Gerasimenko, evidenced by a region of diminished activity from −119 to −6 days before perihelion, that might be interpreted as a topographic effect or the turn off of an active region. (e) We define a photometric parameter (P-AGE) that attempts to measure the relative age of a comet through the activity exhibited in the secular light curve. 81P/Wild 2 (a comet that has recently entered the inner Solar System) is confirmed as a young object, while 28P/Neujmin 1 is confirmed as a very old comet. (f) Arranging the comets by P-AGE also classifies them by shape. A preliminary classification is achieved. (g) The old controversy of what is a nuclear magnitude is clearly resolved.

show abstract

Section: Mean Phase Coefficient For Cometsmentioning

confidence: 87%

Secular light curve of Comet 28P/Neujmin 1 and of spacecraft target Comets 1P/Halley, 9P/Tempel 1, 19P/Borrelly, 21P/Giacobinni–Zinner, 26P/Grigg–Skjellerup, 67P/Churyumov–Gerasimenko, and 81P/Wild 2

Ferrin¹

2007

Icarus

View full text Add to dashboard Cite

show abstract

“…Table II, from Toon et al ., (33) shows the relationship between impact frequency, NEO size, and energy release on impact. (34,35) Overall, current estimates are that objects about 10 m across strike the earth almost annually, with an explosive force of about 10,000 tons of TNT (roughly the yield of the Hiroshima bomb), but break up harmlessly, though noisily, in the atmosphere. Objects about 100 m across, such as the one that exploded over Tunguska, arrive about once every 300 years and could (36) Objects about 1 km across strike the earth once every 500,000 years, and can cause global catastrophic effects and the death of billions.…”

Section: Magnitude Of the Threatmentioning

confidence: 99%

Risks of Hazardous Waste Sites versus Asteroid and Comet Impacts: Accounting for the Discrepancies in U.S. Resource Allocation

Gerrard

2000

Risk Analysis

View full text Add to dashboard Cite

Approximately $6 billion is spent annually in the United States on the cleanup of sites regulated under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, or Superfund). The current health risks posed by such sites are thought to be quite small; the expenditures are justified primarily as protecting hypothetical future residents of these sites. Approximately 0.05% of this amount, or $3 million, is spent annually by the U.S. government on the detection of asteroids or comets that could strike the earth. Such damaging impacts do occur from time to time--most recently in 1908 in an unpopulated region of Siberia--but no person is confirmed ever to have died as a result. Anticipated impacts over the course of 1 million years would yield deaths that, when annualized, total approximately 4,000 per year. The risk reduction goal for CERCLA is 15 orders of magnitude greater than that for asteroid/comet detection. A modest increase in resources devoted to asteroid detection would greatly increase the chances of early detection of a threatening object, allowing an effective defense to be attempted. This article argues that the much lower risk-to-resources ratio for CERCLA cleanups than for asteroid and comet detection can be explained by four primary factors: (1) the regard for future generations, since CERCLA benefits mainly the unborn; (2) concrete fears, since toxics are much more feared than asteroids or comets; (3) the source of the threat, since toxic contamination is caused by human beings, unlike impacts from space objects; and (4) the greater political constituencies for hazardous waste cleanup than for space object detection.

show abstract

“…The Fermi bubbles (Su et al 2010;Ackermann et al 2014), discovered in Fermi Large Area Telescope (Gehrels & Michelson 1999;Fermi-LAT 2022) gamma-ray observations, have finite size and well-defined limits. This suggests their origin is cosmic-ray activity from the inner Galaxy, possibly associated to its supermassive black hole.…”

Section: Introductionmentioning

confidence: 99%

Possible Counterpart Signal of the Fermi Bubbles at the Cosmic-Ray Positrons

Cholis

Krommydas

2023

ApJ

View full text Add to dashboard Cite

The inner Galaxy has hosted cosmic-ray burst events, including those responsible for the gamma-ray Fermi bubbles and the eROSITA bubbles in X-rays. In this work, we study the Alpha Magnetic Spectrometer positron fraction and find three features around 12, 21, and 48 GeV, of which the lowest energy has a 1.4–4.9σ significance, depending on astrophysical background assumptions. Using background simulations that explain the cosmic-ray positron fraction, positron flux, and electron plus positron flux by primary and secondary cosmic rays and cosmic rays from local pulsars, we test these spectral features as originating from electron/positron burst events from the inner Galaxy. We find the 12 GeV feature to be explained by an event of age τ ≃ 3–10 Myr, in agreement with the proposed age of the Fermi bubbles. Furthermore, the energy in cosmic-ray electrons and positrons propagating along the Galactic disk and not within the Fermi bubbles volume is estimated to be 1051.5–1057.5 erg, or O(10−4) − O(1) the cosmic-ray energy causing the Fermi bubbles. We advocate that these positron fraction features are the counterpart signals of the Fermi bubbles, or of substructures within them, or of the eROSITA bubbles.

show abstract

A review of comet and asteroid statistics

Cited by 5 publications

References 39 publications

Secular light curve of Comet 28P/Neujmin 1 and of spacecraft target Comets 1P/Halley, 9P/Tempel 1, 19P/Borrelly, 21P/Giacobinni–Zinner, 26P/Grigg–Skjellerup, 67P/Churyumov–Gerasimenko, and 81P/Wild 2

Secular light curve of Comet 28P/Neujmin 1 and of spacecraft target Comets 1P/Halley, 9P/Tempel 1, 19P/Borrelly, 21P/Giacobinni–Zinner, 26P/Grigg–Skjellerup, 67P/Churyumov–Gerasimenko, and 81P/Wild 2

Risks of Hazardous Waste Sites versus Asteroid and Comet Impacts: Accounting for the Discrepancies in U.S. Resource Allocation

Possible Counterpart Signal of the Fermi Bubbles at the Cosmic-Ray Positrons

Contact Info

Product

Resources

About