From planetaryscience at yahoo.com  Thu Sep 10 22:52:15 2020
From: planetaryscience at yahoo.com (Sam Deen)
Date: Fri, 11 Sep 2020 02:52:15 +0000 (UTC)
Subject: [neo_followup] P115jhg NEA on an interesting orbit
References: <638740488.1020035.1599792735407.ref@mail.yahoo.com>
Message-ID: <638740488.1020035.1599792735407@mail.yahoo.com>

Hi all,

It's been a bit of a while since I've seen an object worth some followup for its interesting orbit. In this case, P115jhg with a ~20 hour arc has an orbit with an interesting eccentricity of definitely >0.6 and nominally about 0.82. High-eccentricity objects aren't too unusual, but with this asteroid's relatively high perihelion distance of 0.84-0.92 AU, as well as its absolute magnitude of only 25.5, this puts it firmly in the surprisingly rare tiny Jupiter-crossing asteroid list- the only dimmer asteroids populating the list being exhaustively: 2007 EE126 (Q = 6.88 AU), 2008 WJ14 (5.58), 2015 KW157 (6.05), 2017 GM (5.75), 2020 FD2 (5.75), and 2020 JA (5.58).

In the interest of followup I'll cut to the chase and put the observation details first (read below for the science case as well)

The asteroid is currently magnitude 21.5 at a decent elongation and a declination that should be accessible from most latitudes. The sigma is less than an arcminute for the entire time it should be visible to most folks here as well, so really the main constraint is the dim magnitude. I would normally be confident it would be followed up, but with only two observatories measuring it, I think it couldn't hurt to get some targeted help for this one.

in late August/early September the asteroid passed quite near Earth, about 1 lunar distance or so, but it came in from the solar side of things with a ridiculous velocity, so that during its brightest period it was moving at around 0.12 degrees a minute. It's currently on its way out again, and will dip below magnitude 22 in about 48 hours, which makes timely followup all the more important.

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The stat ranging (sourced from cneos's scout) for aphelion distances is as such:

aphelion distance (au)    # of clones (out of 1000)
>3                                 1000 (100%)
(3.02 AU find_orb -1 sigma aphelion)
>4                                 993 (99.3%)
>5                                 951 (95.1%)
>6                                 843 (84.3%)
>7                                 708 (70.8%)
>8                                 590 (59.0%)
(8.24 AU find_orb nominal aphelion)
>9                                 473 (47.3%)
>10                               392 (39.2%)
>15                               182 (18.2%)
>20                               103 (10.3%)
>30                               43 (4.3%)
>100                             9 (0.9%)
(e=1.046 find_orb +1 sigma aphelion)

(keep in mind the 1000 clones were constrained to e < 1 so the odds are likely even slightly more in favor of a high aphelion than shown here)

It's worth noting that this asteroid has a >75% chance of having the highest aphelion distance of any asteroid as tiny as it discovered to date (passing the current recordholder 2007 EE126 as listed above) And nominally it far surpasses that, so I think we're looking at a dynamically unique object. Hopefully its quickly approaching magnitude 22 won't stop followup too much.

~Sam