From pluto at projectpluto.com Wed May 5 15:36:41 2021 From: pluto at projectpluto.com (Bill Gray) Date: Wed, 5 May 2021 15:36:41 -0400 Subject: [neo_followup] 2021 GK1 = possible junk Message-ID: Hello all, This is a slightly "slow" object relative to us, the sort of thing that could be either space junk or lunar ejecta. At present, it's a coin toss. If it's junk, it's rather large (H=27.1, possibly bigger), but still within the realm of possible junk sizes. The current astrometry solves to an area/mass ratio of 0.0054 +/- 0.0046 m^2/kg, which is just right for a returning booster. But then again, a rocklike area/mass of essentially zero would also fit about one sigma away. Sometimes, I can run a trajectory backward and say something like "this hasn't been in our neighborhood since Sputnik 1 went up" or "this passed Earth at a date/time suspiciously close to thus-and-such mission." We have a decent arc on this object, but the uncertainties as to where it was become huge after you go back a few decades. So I can neither prove nor disprove that it's junk that way. If it had a small MOID with Mars or Venus, I'd just try to run ephems backward to see if there was an encounter with one of those planets at the time a mission arrived there. No such luck (and the fact that it doesn't seem to be "going anywhere" argues a bit in favor of it being lunar ejecta). I've been keeping an eye on the DOUs for more data as it gets closer to us. There hasn't been any new data since 1 May, and we're now at the point where a few more observations might bring the AMR uncertainty down quite a bit. It's now at about mag 19, and should be at least somewhat visible for another week or so. It won't require much observation, but if you can get a few precise measurements of it during that time, we might be able to settle the junk vs. lunar ejecta question before it leaves our neighborhood. Thanks! -- Bill From pluto at projectpluto.com Sun May 9 21:32:25 2021 From: pluto at projectpluto.com (Bill Gray) Date: Sun, 9 May 2021 21:32:25 -0400 Subject: [neo_followup] TMG0047 = possible artsat Message-ID: Hello all, This object has two solutions. One would be a NEO. The other would be an artsat, in a fairly persuasive one-day orbit. By default, Find_Orb gets the distant, NEO orbit. To get the artsat orbit, run Find_Orb with the observations currently on NEOCP, and set a distance to the object of 70000 km. (You can hit 'r', then enter 70000km.) Do a few Herget steps, then a few full steps (hit 'h' a few times, then hit 'f' a few times). You should see elements that look like this : Orbital elements: TMG0047 Perigee 2021 May 10.267718 +/- 0.00218 TT = 6:25:30.8 (JD 2459344.767718) Epoch 2021 May 10.0 TT = JDT 2459344.5 Gray M 277.546436177 +/- 0.44 (J2000 equator) n 307.986542144 +/- 0.922 Peri. 349.779852 +/- 0.10 a 46872.23685 +/- 93.6 Node 38.556314 +/- 0.030 e 0.58110908 +/- 0.00133 Incl. 26.061983 +/- 0.0027 P1683.16m/1.169d H 32.9 G 0.15 U 12.7 and should be able to generate ephemerides suited to your location. The uncertainties for this object are still manageable, though some larger fields of view may be needed in a few hours. -- Bill From pluto at projectpluto.com Mon May 10 09:49:21 2021 From: pluto at projectpluto.com (Bill Gray) Date: Mon, 10 May 2021 09:49:21 -0400 Subject: [neo_followup] 2021 GK1 = possible junk In-Reply-To: References: Message-ID: <3c268d52-1fd7-7d41-970d-4ebc2f43b078@projectpluto.com> Hi folks, A follow-up to this post. We did get two more tracklets on it on May 4 and 5, thanks to (703) Catalina and (Y00) SONEAR (thank you!) That helped. It looks as if there may have been encounters in the late 1960s. More data would help. The object is currently going around at perigee, headed to lower elongations, and will soon be effectively invisible for a while. That may be especially true if it's an artsat; those seem to get faint more quickly at high phase angles than rocks do (not always, but often). One small incentive for me to revise Find_Orb to determine G and/or G1 and G2 magnitude parameters is that "oddball" slope parameters might hint at non-rock-ness. I mention this because if you've tried for 2021 GK1 and failed, or _do_ try for it and don't see it, I'd like to hear from you; it would be added evidence that this is indeed not a rock. A few weeks after perigee, it'll come back out where the big scopes can get it at faint magnitudes. But some data now, near perigee, would fill in a gap in the orbital arc that might give us a more solid value for non-gravitational parameters, and perhaps a good enough orbit to identify the object. Should note that I really ought to have sent this e-mail yesterday. The object is down at mag 19.5 already (if it's a rock), and will quite soon be at low enough elongations to make observing difficult to impossible. Thanks! -- Bill On 5/5/21 3:36 PM, Bill Gray wrote: > Hello all, > > ?? This is a slightly "slow" object relative to us,? the > sort of thing that could be either space junk or lunar > ejecta.? At present,? it's a coin toss.? If it's junk, > it's rather large (H=27.1,? possibly bigger),? but still > within the realm of possible junk sizes. > > ?? The current astrometry solves to an area/mass ratio > of 0.0054 +/- 0.0046 m^2/kg,? which is just right for a > returning booster.? But then again,? a rocklike area/mass > of essentially zero would also fit about one sigma away. > > ?? Sometimes,? I can run a trajectory backward and say > something like "this hasn't been in our neighborhood since > Sputnik 1 went up" or "this passed Earth at a date/time > suspiciously close to thus-and-such mission."? We have a > decent arc on this object,? but the uncertainties as to > where it was become huge after you go back a few decades. > So I can neither prove nor disprove that it's junk that way. > > ?? If it had a small MOID with Mars or Venus,? I'd just try > to run ephems backward to see if there was an encounter > with one of those planets at the time a mission arrived > there.? No such luck (and the fact that it doesn't seem > to be "going anywhere" argues a bit in favor of it being > lunar ejecta). > > ?? I've been keeping an eye on the DOUs for more data as > it gets closer to us.? There hasn't been any new data > since 1 May,? and we're now at the point where a few more > observations might bring the AMR uncertainty down quite a > bit. > > ?? It's now at about mag 19,? and should be at least somewhat > visible for another week or so.? It won't require much > observation,? but if you can get a few precise measurements > of it during that time,? we might be able to settle the junk > vs. lunar ejecta question before it leaves our neighborhood. > > Thanks!??????????? -- Bill