WELCOME BACK, HERMES
==================
2003 October 17
John Pazmino
NYSkies
john.pazmino@moondog.com
[I cobbled this article from several diverse sources, so the writing
style is uneven.]
After eluding astronomers for 66 years, the long-lost asteroid Hermes
has finally been retrieved.
Early on 2003 October 15, Brian Skiff, Lowell Observatory Near-Earth
Object Search (LONEOS), sent measurements of four CCD images obtained
with the 58cm Catalina Schmidt telescope to the Minor Planet Center
in Cambridge, Massachusetts. At the Center, Timothy Spahr identified
the suspect with other measurements submitted in the past seven weeks --
but not recognized as unusual -- by LONEOS and by the Lincoln Near
Earth Asteroid Research (LINEAR) project. In addition, quick action by
James Young, Table Mountain Observatory, secured a confirmation just
before dawn on the 15th.
A bright near-earth-object candidate, reported this morning by B.
Skiff, was placed on The NEO Confirmation Page by T B Spahr quickly
enough that follow-up observations could be made by J Young within
four hours. Spahr then located the Oct 5 observations (which had been
reported as a likely main-belt object) and recognized the object as
1937-UB (Hermes). With the help of the LINEAR Team, single-night
observations (also reported as likely main-belt objects) could then be
identified back to Aug 26. The initial orbital elements, omitted here,
have not been linked to the 1937 observations, since when the object
has made almost exactly 31 revolutions. Radar observations at the
present apparition would be very useful.
Judging by its brightness, Hermes is a minor planet about 1 to 2
kilometers across. So it could be somewhat larger than the 1937
estimates. In a famous exhibit at the American Museum of Natural
History, New York, Hermes was depicted as a sphere about the size of
Central Park.
Hermes is by far the most famous of "lost asteroids". It was
discovered by Karl Reinmuth at Heidelberg, Germany, on 28 October
1937 and tracked for only five days. Although never officially
numbered, it has been known by the name Hermes or catalog number 1937-
UB ever since.
In late October 2003, Hermes will be bright enough (magnitude 13)
to be seen in 20cm and larger amateur telescopes as it races westward
across Cetus, Pisces, and Aquarius. By month's end it will be moving 7
degrees per day and gaining. Unlike the situation in 1937, when Hermes
skimmed to within 800,000 km of our planet (two Earth-Moon distances),
it will pass about nine times that far on 4 November 2003.
Nevertheless, the possibility of future close encounters definitely
puts this object in the Potentially Hazardous Asteroid class.
The discovery was announced on Minor Planet Electronic Circular
2003-T74, issued 2003 October 15, with the inital observations from
LINEAR and LONEOS:
Observations of 1937-UB (Hermes)
Object -----UT Date----- RA------(2000)------dec Magn Obs
J37U00B C2003 08 26.35985 01 52 54.33 +04 08 41.6 18.8 704
J37U00B C2003 08 26.37269 01 52 54.87 +04 08 44.8 19.6 704
J37U00B C2003 08 26.38603 01 52 55.52 +04 08 46.6 19.3 704
J37U00B C2003 08 26.41142 01 52 56.62 +04 08 52.1 19.2 704
J37U00B C2003 09 03.37679 01 58 49.08 +04 23 54.8 19.0 704
J37U00B C2003 09 03.38860 01 58 49.59 +04 23 55.5 19.1 704
J37U00B C2003 09 03.40035 01 58 49.96 +04 23 55.8 18.6 704
J37U00B C2003 09 03.41219 01 58 50.36 +04 23 57.0 19.3 704
J37U00B C2003 09 28.29353 02 05 19.55 +04 12 35.4 16.9 704
J37U00B C2003 09 28.30707 02 05 19.22 +04 12 32.1 18.5 704
J37U00B C2003 09 28.31989 02 05 18.78 +04 12 30.5 18.0 704
J37U00B C2003 09 28.34613 02 05 18.17 +04 12 26.7 17.0 704
J37U00B C2003 09 28.37929 02 05 17.41 +04 12 21.0 17.1R 699
J37U00B C2003 09 28.39356 02 05 17.02 +04 12 18.8 699
J37U00B C2003 09 28.40779 02 05 16.65 +04 12 15.9 699
J37U00B C2003 09 28.42207 02 05 16.31 +04 12 14.2 699
J37U00B C2003 10 05.59036 02 01 02.22 +03 46 56.7 16.7 608
J37U00B C2003 10 05.60121 02 01 01.55 +03 46 53.9 16.8 608
J37U00B C2003 10 05.61168 02 01 00.90 +03 46 50.5 16.8 608
J37U00B C2003 10 15.30771 01 45 29.04 +02 45 15.7 14.4R 699
J37U00B C2003 10 15.32432 01 45 26.23 +02 45 06.8 699
J37U00B C2003 10 15.34094 01 45 23.44 +02 44 57.8 699
J37U00B C2003 10 15.35751 01 45 20.63 +02 44 48.9 699
J37U00B C2003 10 15.51076 01 44 55.17 +02 43 26.6 14.5R 673
J37U00B C2003 10 15.51215 01 44 54.94 +02 43 25.8 673
J37U00B C2003 10 15.51354 01 44 54.72 +02 43 24.9 673
J37U00B C2003 10 15.51516 01 44 54.47 +02 43 24.2 673
J37U00B C2003 10 15.51725 01 44 54.14 +02 43 23.1 673
Obs Details:
608 Haleakala-NEAT/MSSS. R Bambery, E Helin, S Pravdo, M Hicks,
K Lawrence, P Kervin, J Africano, R Maeda. 1.2-m reflector +
CCD.
673 Table Mountain Observatory, Wrightwood. J Young. 0.6-m
reflector + CCD.
699 Lowell Observatory-LONEOS. M E Van Ness, B A Skiff. 0.59-m
LONEOS Schmidt + CCD.
704 Lincoln Laboratory ETS, New Mexico. M Blythe, F Shelly,
M Bezpalko, R Huber, L Manguso, D Torres, R Kracke, M McCleary,
H Stange, S Adams, T Brothers, S Partridge. Measurers J Stuart,
R Sayer, J Evans, J Kommers, P Hopman. 1.0-m f/2.15 reflector +
CCD.
The orbit for Hermes was dynamically linked from 1937 to 2003 by
Steven Chesley and Paul Chodas, Jet Propulsion Laboratory, and issued
2003 October 16. Using sophisticated orbit determination tools, the
difficult problem of finding a precise orbit for the long-lost and
recently rediscovered asteroid Hermes has been solved.
The recovery of Hermes was announced on 15 October 2003 by the
Minor Planet Center in Cambridge, Massachusetts. The object was
initially noted by Brian Skiff of the LONEOS asteroid search program
at the Lowell Observatory in Arizona, and key follow-up measurements
were provided by James Young of JPL Table Mountain Observatory in
California. Tim Spahr of the MPC located prediscovery observations
from the last 7 weeks and computed the new object's orbit. Noticing
that the orbit was very similar to that of Hermes, last seen during
its close approach in 1937, Spahr concluded that the new object was
almost certainly Hermes. Definitive proof of the object's identity was
still lacking, however, because an orbit linking the known positions
in 1937 to those in 2003 could not be found.
Finding the precise orbit of Hermes is difficult because its
trajectory is very chaotic. In the 66 years since it was last seen,
the asteroid has made numerous close approaches to both the Earth and
Venus. Since the orbital changes at each approach depend highly on the
circumstances of the encounter, finding an orbit with the precise
sequence of encounter conditions that links positions in 2003 to those
in 1937 is a challenging problem in orbit determination.
We have now solved this problem by using the JPL Sentry impact
monitoring software in a novel way. Starting from the 2003 positions,
Sentry found twelve distinct dynamical pathways that produced
encounters in 1937, each with a different sequence of intervening
close approach circumstances. Comparing thes e predicted 1937
encounters with the one determined directly from the 1937
observations, we were able to identify the most consistent candidate,
and then zero in on the precise orbit that best matches the positions
in both 1937 and 2003. We now know that since it was last seen, Hermes
has made eight close approaches to the Earth and Venus to within 0.06
AU, including an Earth approac h to within about 1.6 lunar distances
in 1942. The new orbit solution allows us to predict future close
approaches with great accuracy; we can now predict that Hermes will
not approach the Earth any closer than about 0.02 AU (8 lunar
distances) within the next hundred years.
The orbital elements and ephemeris below have been adapted from
Minor Planet Electronic Circular 2003-U04, issued 2003 October 16.
Orbital elements by Chesley and Chodas for 1937-UB (Hermes)
Epoch 2003 Dec 27.0 TT = JDT 2453000.5
MAn 1.79511 (2000.0)
MDM 0.46297069 ArgP 92.39489
SMA 1.6548821 AscN 34.51690
Exc 0.6241613 Incl 6.06802
Per 2.13 yr H 17.5 G 0.15 U 2
Ephemeris for 1937-UB (Hermes) at 0h TT
2003 RA---(2000)---Dec EH-AU SH-AU Elong PAng Magn
10 08 01 58.54 +03 35.4 0.287 1.277 163.4 12.9 16.1
10 09 01 57.29 +03 30.0 0.275 1.267 164.6 12.1 15.9
10 10 01 55.90 +03 24.3 0.264 1.256 165.7 11.3 15.8
10 11 01 54.35 +03 18.1 0.253 1.246 166.9 10.5 15.7
10 12 01 52.63 +03 11.4 0.242 1.236 168.0 9.7 15.5
10 13 01 50.73 +03 04.3 0.231 1.226 169.1 8.8 15.4
10 14 01 48.61 +02 56.6 0.221 1.216 170.2 8.0 15.2
10 15 01 46.26 +02 48.3 0.210 1.205 171.2 7.3 15.0
10 16 01 43.64 +02 39.3 0.200 1.195 172.0 6.7 14.9
10 17 01 40.72 +02 29.6 0.189 1.185 172.5 6.3 14.7
10 18 01 37.45 +02 18.9 0.179 1.174 172.7 6.2 14.6
10 19 01 33.78 +02 07.2 0.169 1.164 172.4 6.5 14.5
10 20 01 29.64 +01 54.2 0.159 1.153 171.6 7.2 14.3
10 21 01 24.96 +01 39.8 0.149 1.143 170.4 8.4 14.2
10 22 01 19.63 +01 23.7 0.139 1.132 168.7 9.9 14.1
10 23 01 13.53 +01 05.6 0.130 1.122 166.7 11.7 14.0
10 24 01 06.49 +00 45.0 0.120 1.111 164.4 13.9 13.9
10 25 00 58.31 +00 21.4 0.111 1.101 161.7 16.5 13.8
10 26 00 48.73 -00 05.8 0.102 1.090 158.5 19.5 13.7
10 27 00 37.38 -00 37.7 0.094 1.079 154.9 23.0 13.6
10 28 00 23.83 -01 15.1 0.085 1.069 150.7 27.1 13.5
10 29 00 07.47 -01 59.5 0.077 1.058 145.7 31.9 13.4
10 30 23 47.56 -02 52.2 0.070 1.048 139.9 37.7 13.3
10 31 23 23.19 -03 54.3 0.063 1.037 132.9 44.5 13.3
11 01 22 53.42 -05 05.9 0.057 1.026 124.6 52.8 13.3
11 02 22 17.57 -06 24.6 0.052 1.015 114.8 62.5 13.4
11 03 21 35.82 -07 43.6 0.049 1.005 103.5 73.7 13.6
11 04 20 49.83 -08 52.4 0.048 0.994 91.3 85.9 13.9
11 05 20 02.86 -09 40.6 0.048 0.983 78.9 98.3 14.4
11 06 19 18.55 -10 04.2 0.051 0.973 67.2 110.0 15.1
11 07 18 39.48 -10 06.9 0.055 0.962 56.8 120.4 16.0
In the table Hermes's distance from the Earth (EH-AU) and Sun (SH-
AU) is in astronomical units. Its elongation angle from the Sun
(Elong), angle of Hermes from the Earth as seen from the Sun (PAng)
are in degees. The visual magnitude (Magn) is based on assumed size
and albedo of hermes.
The orbit above is based on a computation linking the 1937 and
2003 observations by S R Chesley and P W Chodas of NASA NEO Program
Office at the Jet Propulsion Laboratory. They note that the trajectory
of 1937-UB is very chaotic due to frequent and close planetary
encounters. Between the 1937 October encounter at 0.00495 AU and the
present encounter, 1937-UB made eight intervening close approaches to
the Earth or Venus at distances less than 0.06 AU, including an
approach to within 0.0043 AU of Earth on 1942 April 26.7.
These perturbations dramatically narrowed the region of
convergence for differential corrections, so that very precise initial
conditions were required to permit a least-squares fit. With the use
of just the 2003 astrometry the JPL Sentry impact monitoring software
(which was specifically developed to cope with such extreme
nonlinearity) identified twelve dynamically distinct routes from 2003
to the 1937 encounter. Comparing target plane projections of these
possibilities with that of the observed 1937 encounter enabled them to
derive suitable initial conditions permitting a general orbital
solution using all data, with appropriate weighting of the low-quality
1937 data.