2007 September notes: 2007 RJ1, 2007 SU1 and 2007 RS1

Plenty of clear nights in September with quite a lot of activity from the surveys on the NEO Confirmation page. Indeed, around September 17th there were 32 objects listed, which may be a record.

Several close approaches were observed during the month, including 2007 RJ1 which was followed for 12 days and ended up at 2.8 Lunar Distances (LD) on Sep 16.1UT moving at 102"/min. 2007 SU1 was seen at 6 LD, moving at 44"/min on Sep 27.0UT.

However, the headline object for me was 2007 RS1 on Sep 4th. This tiny NEO was discovered by Steve Larson using the 1.5-m Mt. Lemmon Catalina Sky Survey telescope just before 6am UT on the 4th. It was unusually faint at mag. +20.4 considering it was already moving at 13"/min. Steve managed to track it for over 3 1/2 hours, by which time it had accelerated to a speed of 19"/min and brightened by half a magnitude.

By the time the sky was getting dark at Great Shefford later that day 2007 RS1 was already closer than 1 LD and moving at 150"/min but had not been reported since the Mt Lemmon observations. The positional uncertainty on the sky was rapidly getting worse and predicted by the Minor Planet Center to be about 3.5 degrees at 20:00 UT (11 times larger than my field of view) and set to double in size within the next 70 minutes. I started trying to cover the uncertainty area, starting at the nominal position, but after taking just a couple of fields got a phone call that I needed to pick my daughter up from Newbury (a 20 mile round trip). All I could do was to set the telescope some distance ahead of the predicted place and let it take images while I was away, hoping that the object might just pass through my 18'x18' field of view. I set the exposure length to 4 seconds which would cause the object to trail if it did pass through, making it more obvious to identify but at the expense of some accuracy in measurement.

Background stars appear as lines of dots as the fast moving asteroid is kept in the centre of the image and itself appears as a small streak due to its own movement during each individual exposure

By the time I returned from Newbury the sky was clouding over for the night but I had amassed a total of 756 images, 564 taken in one long sequence while I was driving. After spending a number of hours searching the images I eventually managed to locate the tell-tale streaks of the NEO speeding through some of the images taken while I was away from the observatory. Remarkably it passed almost centrally through the field of view, taking just four minutes to pass from one side to the other. With the ephemeris corrected I was then able to find a few more images of it entering the field of view at the very end of one of the early runs I took before I left.

The last images that recorded it were taken at 20:39 UT when it was mag +18, moving at 246"/minute and with it 0.55 LD from Earth. It was to pass just 0.19 LD from Earth, or less than 6 Earth diameters away at 01:18 UT on September 5th, but was it was not reported again.

JPL is listing 2007 RS1 with the faintest absolute magnitude of any Minor Planet, with H = 30.98 +/-0.36, the previous record being 2003 SQ222 at H = 29.99 +/-0.70. It is likely that 2007 RS1 is only about 1 or 2 meters in diameter.

2007 August notes: 2007 QA1

August saw a rash of new main belt objects picked up from Great Shefford and as I write this four have very good, secure orbits, three others are OK with several weeks of observations and one I only managed to record on two nights and so is effectively lost.

2007 QA1 was another new object I picked up on the night of Aug 16 at mag +19.0 which turned out to be interesting - it was heading almost due south (in p.a. 195 deg) though was not moving unusually fast. I could not identify it with any known object on the MPCs Minor Planet Checker web page. I also checked it against the MPCs NEO rating page to see if it had any chance of being a NEO and that came back with a very low rating of 3% (50%+ is required to get an object placed on the NEO Confirmation Page). I held onto the positions to try and get a second night but the next night was cloudy.

Later that day the MPC added it to the NEOCP, having received positions from the Lowell Observatory. Although it did not end up being a NEO (perihelion distance was just greater than the 1.3 AU limit) it was a Mars crosser and having appeared on the NEOCP from Lowell it was effectively lost to me as a discovery - the first observatory reporting even a single night of observations will be granted discovery credit if it appears on the NEOCP, unlike normal Main Belt objects where it is generally the first observatory to report two nights of positions that gets discovery credit.

Lesson learned: Don't rely on the NEO rating page to decide if an object is interesting! In fact it's motion was very unusual, of the 1794 minor planets that were mag +23 or brighter within 5 degrees of 2007 QA1, only one other was moving in a direction with a p.a. less than 209 degrees. Next time(and I hope there is one!) if another potentially interesting object turns up I will submit a single night of positions to the MPC and let them decide whether it is interesting enough to put on the NEOCP...

2007 July notes: Floods, 2007 DT103, 2007 MB4 and recovery of 2001 RV17, 2005 XW77 and 2003 CG11

The continued bad weather here culminated in flash flooding on 20th July which left us with two rooms under water, but fortunately the observatory stayed dry. Since then the weather has noticably improved with a run of good clear nights in the last week of the month.

During the month three NEOs were recovered at their second apparition - 2001 RV17 at the beginning of the month with 2005 XW77 and 2003 CG11 towards the end, both of those two in collaboration with Luca Buzzi at the Schiaparelli Observatory in Italy.

A couple of moderately fast movers were followed over several nights - 2007 DT103 which was detected at the end of the month by RADAR from Goldstone and found to be a binary, and 2007 MB4 that passed at about 8 Lunar Distances on July 5th.

2007 June notes: 6R10DB9's fourth and final perigee

As anyone in the UK will already know, the poor weather in May just got worse through June. I suffered the least number of hours observing since December 2002.

The unusual object with provisional designation 6R10DB9 made it's fourth and final perigee in June. Back during the March perigee it was observed with the 10-m SALT telescope and found to have a rotation period of only 2.75 minutes and an amplitude at that time of 1.2 magnitudes. This time it approached from the sunward side of the Earth, passed over the North pole and was picked up again a day after perigee on June 15th in Draco, about 1 degree from Theta Cep while only 0.80 Lunar Distances from Earth, magnitude +19 - +20 and moving at 47"/min. Never 'bright', it was recorded at mag +18.6 on June 18th and at about +19.5 on the 20th, fading again as it receded from both Sun and Earth. The only other observations reported at the time of writing are radar detections from Goldstone on June 12 & 14 and optical astrometry from the 1.5-m Mt Lemmon telescope on June 22. By the end of June it was below 20th mag and too far south to attempt from the UK.

The main indicator that this object is likely to be natural rather than a piece of artificial space junk come from determinations of solar radiation pressure (SRP) acting on it. Bill Gray's FindOrb freeware program includes routines to calculate SRP, given as the area-to-mass ratio or AMRAT in m^2/kg. With astrometry extending for 10 months now, it gives a value of 0.0011, with an RMS residual from 132 observations of 2.5". Not including SRP increases the RMS residual to an unsatisfactory 9.1". The JPL Horizons orbit solution which also includes the Goldstone Radar observations, gives an even smaller value of AMRAT of 0.0007. In comparison, various distant artificial satellites, such as IMP8, Geotail, J002E3 (the piece of old Apollo hardware discovered by Bill Yeung in 2003), WMAP etc have values between 10 and 50 times larger, indicating that 6R10DB9 is much more massive and much less prone to the perturbing effects of SRP than artificial satellites and is therefore likely to be a rocky body, probably about 4 metres in diameter. There is still a chance that time might be spent at some of the large observatories to get spectra and other measurements during July before it goes out of range completely.

2007 April notes: 2007 HV4, Comet C/2007 H2 Skiff, 2007 HB5

April provided at least some observing at the telescope on 20 nights, though a fair proportion were of poor quality with haze or moonlight (or both).

Even so there were some notable objects followed. Apollo 2007 HV4 was confirmed on the NEO Confirmation Page during the evening of April 20th, discovered earlier the same day by the Mt. Lemmon operation of the Catalina Sky Survey. When found it was only 5 times further away than the Moon and a difficult discovery at mag +20.5, moving at 14"/min. When confirmed 16 hours later it had already doubled in apparent speed and was about 1 magnitude brighter. Although never brighter than 18th mag, it was followed over the next two nights reaching a speed of over 180"/min during the evening of April 22nd, 5 hours after passing Earth at 1.4 Lunar Distances.

Another NEO Confirmation Page object observed on the evening of April 19th turned out to be an 18th mag comet (later designated C/2007 H2 Skiff), announced the next day by the Minor Planet Center (MPC) on MPEC 2007-H33. The comet was moving north at 3"/min but later, when the images were checked for other moving objects (by stacking for main belt minor planet motion of 0.5"/min in a westerly direction), a minor planet could be seen about 4' north of the comet. The comet passed a mere 23" west of the minor planet at about 23:00 UT that night.

Using Astrometrica and the MPCs Minor Planet Checker web page it could not be matched with a known object, so the next night the unidentified object was picked up again and the details of both nights were sent off to the MPC. The MPC could not ID it with a known object, assigned it provisional designation 2007 HB5 and gave Great Shefford discovery credit for this main belter. This is a good example of making use of the images taken for a different purpose - on the discovery night five other observatories reported positions for C/2007 H2 around the same time as I did, but only one, Juan Lacruz at La Canada (J87) in Spain also reported positions for 2007 HB5 that night.