Observation arc
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In
Short arcs
A very short arc leaves a high
A relatively modest observation arc may allow finding an older "precovery" photo, providing a much longer arc and a more precise orbit.
An observation arc less than 30 days can make it difficult to recover an
As a general rule objects discovered when they are currently farther from the Sun will have greater uncertainties in their initial orbits if the observation arcs are short.
2018 AG37 which was discovered when 100+ AU from the Sun and has only been observed 9 times over 2 years[2] will require an observation arc of several years to refine the uncertainties in the orbital period and aphelion (farthest distance from the Sun).
1999 DP8 with only 4 observations over 1 day[3] has uncertainties so large that the error bars are not really meaningful and just show that the uncertainties are very large. On its discovery date 1999 DP8 is estimated to have been 52±1500 AU from Earth.[3]
It took an observation arc of about 200 days to rule out a Mars impact by Oort cloud comet C/2013 A1 (Siding Spring).[5]
Interstellar objects
Earth approaches
Comet | Observation arc |
Number of observations |
Uncertainty parameter |
Earth approach date |
Uncertainty in distance from Earth |
Reference |
---|---|---|---|---|---|---|
Comet Swift–Tuttle | 257 years | 652 | 0 | 2126-Aug-05 | ±10 thousand km | data |
C/2001 OG108 |
0.9 years | 886 | 2 | 2147-Mar-23 | ±2 million km | data |
C/1991 L3 (Levy) | 1.6 years | 125 | 3 | 2094-Aug-01 | ±15 million km | data |
With an observation arc of 257 years, the uncertainty in
In contrast, comet C/2022 A1 (Sarneczky) was discovered on 2 January 2022 when it was 1.3 AU from the Sun, and announced on 7 January 2022 with only a 5-day observation arc.[10] It made its closest Earth approach the next day with a 3-sigma uncertainty region of ±1 million km.[11] The large uncertainty was a result of the short arc and discovery distance.
See also
References
- ^ TNOs really do require patience; 2-3 years is only just enough to say anything about the orbit parameters – Astronomer Michele Bannister (4 April 2018)
- ^ JPL Small-Body Database Browser for 2018 AG37
- ^ a b JPL Small-Body Database Browser for 1999 DP8. Discovery date Ephemeris table setting: #39. Range & range-rate = 6.8E+11 / AU / 3-sigma = 1500 AU
- IAU Minor Planet Center. 2017-05-24. Retrieved 2017-10-21. (CK17K020) T 2027 Jan. 5
- ^ "How to determine the orbit of a comet?". esa. 2014-03-07. Retrieved 2022-01-08.
It took 44 days of observation to achieve even a semblance of an orbit determination – one that was still all over the place
- ^ JPL Small-Body Database Browser for C/2008 J4 (McNaught)
e = 0.9977 to 1.017
semi-major axis = −58
v=42.1219 √1/50000 − 0.5/−58 - ^ JPL Small-Body Database Browser for C/1999 U2 (SOHO)
- ^ JPL Small-Body Database Browser for Comet Swift–Tuttle
- ^ JPL Small-Body Database Browser for C/2001 OG108
(Close approach uncertainty: (MaxDist of 0.434) – (MinDist of 0.408) * 149597870.7 = 3.9 million km) - IAU Minor Planet Center. 2022-01-07. Retrieved 2022-01-08. (CK22A010)
- ^ C/2022 A1 (Sarneczky) Close approach table at JPL SBDB and Uncertainty region archive
External links
- How to determine the orbit of a comet? (ESA 7 March 2014)
- Asteroid Hazards, Part 2: The Challenge of Detection on YouTube(min. 7:14)
- Asteroid Hazards, Part 3: Finding the Path on YouTube(min. 5:38)