When observing a comet please try to forget how bright
you think the comet should be, what it was when you last viewed
it, what other observers think it is or what the ephemeris says
it should be.
The equations for the light curves of comets that are
currently visible use only the raw observations and should give a
reasonable prediction for the current brightness. If the comet
has not yet been observed or has gone from view a correction for
aperture is included, so that telescopic observers should expect
the comet to be fainter than given by the equation. The
correction is about 0.033 per centimetre. Values for the r
parameter given in square brackets [ ] are assumed. The form of
the light curve is either the standard m = H0 + 5 log d + K0 log
r or the linear brightening m = H0 + 5 log d + L0 abs(t - T + D0)
where T is the date of perihelion, t the present and D0 an
offset, if L0 is +ve the comet brightens towards perihelion and
if D0 is +ve the comet is brightest prior to perihelion.
Sam Deen has identified several objects that seem to show clear evidence of a cometary nature, but which have not
yet been recognised by the MPC. These were described in a post on the
comets-ml on 2021 April 7, with additional objects described on May 23, September 29
and 2022 December 15.
In the following entries "I" refers to Sam Deen.
A/Palomar = 2012 KA51
2012 KA51 was discovered on 2012/05/22 by the Palomar Transient Factory (PTF) and observed for only a week without being recovered. I found many more
unmeasured observations from PANSTARRS which showed it to be a highly eccentric object with a perihelion of 4.896 au and an aphelion of 959 au.
in all of these observations it appears noticeably elongated (or too faint to make out features anyway). Furthermore, investigating the original PTF
images shows it as rather noticeably fuzzy.
A/PanSTARRS = 2017 DJ
To quickly preface, this one might not be a comet. The evidence for activity is suspect, but looks strong enough for me to include anyway.
2017 DJ was discovered on 2017/02/17 by PANSTARRS and observed for just 2 days without recovery. I extended the arc to 21 days, enough
to calculate a rudimentary orbit with P=5.84 years and q=1.76 au. Although there are no accessible observations near its perihelion
(the last high-quality observation is February 21 (r = 1.84)) the observations do show it being visibly hazier than surrounding stars.
Luckily it shouldn't remain ambiguous for too long, as 2017 DJ will be returning in early 2023 with some slightly more favorable geometry
to allow us to observe it nearer to perihelion.
A/PanSTARRS = 2017 GZ8
A/PanSTARRS = 2017 MC9
2017 MC9 was discovered on 2017/06/22 by PANSTARRS and observed for 11 days without being recovered. I found a very extensive set of W84 observations
going into September, still not published, which give a robust orbit with P=6.23 years and q=1.61 au.
It appears reliably fuzzy with a tail pointing west and then northwest on 2017/07/02 (r=1.61), 2017/07/03 (r=1.61), 2017/07/17 (r=1.61), and 2017/08/25 (r=1.67),
but not on 2017/09/02 (r=1.69). None of this is too surprising, as running its orbit back shows that it had a much higher perihelion distance of 2.1 au until
the early 1800s, and then ~1.85 until the 1940s. Its 2017 perihelion was actually its closest yet to the Sun, and it looks like as close as it's going to get
for a while as it oscillates between 1.6 and 1.7 au for the next couple centuries.
A/PanSTARRS = 2017 PY24
2017 PY24 was discovered on 2017-08-07 by PANSTARRS and observed for about a month, the last (previously published) observation from 4 days before perihelion.
I found a number of observations purposefully made of the comet, but never reported for some reason, between December 2017 and January 2018,
in all of which it is an extremely clear-cut case of a comet, with the peculiarity that its tail seems consistently separated from the comet head itself.
With a period of 72 years, it's a definite Halley-type comet.
A/PanSTARRS = 2017 YL4
2017 YL4 was discovered on 2017-12-24 by PANSTARRS and observed for just two days before being lost. I was recently able to find many more observations
showing it as very obviously as a long period comet (P = 1900 yr). On 2018/02/11, the object appeared obviously cometary, with a decently condensed coma
with a FWHM of around 1.0 arcsecond (the seeing isn't reported but I would visually estimate 0.4 arcseconds). The tail is 8 arcseconds long and mildly
curved, stretching south at a PA of around 155-165.
A/LINEAR = 2005 YB210
This asteroid was discovered by LINEAR about two years after perihelion, with prediscovery observations found from 2004. It was recovered in 2019 by
PanSTARRS. Sam found additional images from 2013, and from 2019. The magnitude of the object is quite variable between 19 and 23, suggestive
of cometary outbursts, though none of the images shows tail or coma.
A/Lemmon = 2008 BJ22
This asteroid was discovered by the Mt Lemmon Survey in images taken with the 1.5m
reflector on 2008 January 31.38. Until Sam Deen chased down further positions it was regarded as
a normal Main-belt asteroid. The additional observations showed a distinct tail in 2008 Subaru, 2009 PTF and 2013 DECam images.
Sam suggests that the asteroid completely disintegrated in 2008, leaving only the debris trail. The disintegration could be
due to an impact or YORP spin-up.
A/Palomar = 2010 LN135
This object was discovered by the Palomar (Zwicky) Transient Factory on 2010 June 4.29 at 21st magnitude. It is in a near parabolic orbit,
with perihelion at 1.7 au in 2011 May, when it might
have reached 16th magnitude. Curiously no observations were made after 2010 August 15. PanSTARRS images taken on that date show a coma and possible
tail. Although the PTF observers recognised it as a comet at the time, it was never acknowledged by the MPC.
A/Lemmon = 2010 DJ10
This asteroid was discovered by the Mt Lemmon Survey in images taken with the 1.5m
reflector on 2010 February 16.39. Until Sam Deen chased down further positions it was regarded as
a Main-belt Mars-crossing asteroid. The additional observations show that it is in a Jupiter and Saturn
crossing orbit with perihelion at 2.8 au and period of 17 years.
A/PanSTARRS = 2018 BJ11
This asteroid was discovered by PanSTARRS on 2018 January 20.33 at 22nd magnitude. There were pre-discovery PanSTARRS images from
2017 November 20 and 2018 January 11. The object was followed until February 9. It was at perihelion in 2015 November at 3.2 au
and has a period of 8.5 years. In 2023 June K Ly found a DECam image from 2018 March 8 that shows a diffuse coma. It can approach
Jupiter to within 0.4 au.
A/Lemmon = 2023 JN16
This asteroid was discovered at 19th magnitude by the Mt Lemmon Survey in images taken with the 1.5m
reflector on 2023 May 10.23. The brightness and lack of pre-discovery observations was
suggested by Peter VanWylen to indicate a possible main belt comet. Sam Deen, Arndt Schnabel and K Ly made
follow-up observations and detected clear signs of cometary activity on June 16. It was at perihelion in 2020 July
at 2.3 au and has a period of 4.4 years in a low eccentricity orbit, which gives no particularly close planetary approaches.
It returns to perihelion in 2024 December.
A/PanSTARRS = 2014 VF40
2014 VF40 was discovered on 2014 November 10.41 by PANSTARRS and has been observed over one orbit. It has a period of 7.3
years and perihelion at 1.9 au. It passed 0.3 au from Jupiter in 2021 February. Mike Kelly reported on the comets-ml that it was showing
active behaviour in ZTF images from 2023 October onwards.
CBET 2583, issued on 2010 December 12, announced the discovery of a spiral like structure
around main belt asteroid (596) Scheila by Steve Larson in the course of Catalina Sky Survey
(CSS) with the Catalina 0.68-m Schmidt telescope, on images obtained on 2010 December 11.44.
The cometary appearance has been confirmed by other observers. In the Catalina images, the
"coma" is bright (~13.5 compared to the expected 14.2), and extends some 2 arcmin north and 5 arcmin west from the
central condensation in a spiral like structure reminiscent of 29P in outburst. Recent images show a stellar
appearance in October and November, but slight diffuseness on December 3.4.
Radio observations from Arecibo between mid December and early January show no clear detection of OH emission in the 1667 MHz line. This
may suggest that the cometary appearance was due to an impact event, or simply that gas emission was very weak.
al in a paper submitted to ApJL suggest that the activity was most likely due to impact
with a 35m diameter body.
The "Dictionary of
Minor Planet Names" notes that (596) Scheila was discovered on 1906 February 21 by A. Kopff at
Heidelberg. Named in honor of an acquaintance of the discoverer, a female English student in Heidelberg.
(596) Scheila is a main-belt asteroid inclined roughly 14 degree on the ecliptic and it is now 3.1AU from the Sun and 2.5AU
from the Earth. It is next at perihelion in 2012 May and has a period of 5.0 years. Its distance from the sun varies
between 2.4 and 3.4 AU. It is about 117km diameter and has an abledo of 0.036.
Alan Hale noted on the comets-ml [2021 August 27] that a paper by Busarev et al reported possible detection of ice sublimation from
the asteroid whilst near perihelion in 2012. So far he had not detected any evidence of a coma or tail at the 2021 return, when
perihelion is in December. Sam Deen then noted that it is in a Kozai resonance with Jupiter and that the perihelion distance has been
slowly reducing for the last few millenia. It is currently near its minimum of 1.4 au.
Asteroid (3200) Phaethon has perihelion at 0.14 AU and has been suggested as a possible extinct comet nucleus. It is the parent body of the Geminid meteors.
It was imaged by STEREO during its 2009 perihelion and appears to have been significantly brighter than expected at around the time of perihelion (June 20),
suggesting the possibility of cometary activity.
K. Battams, Naval Research Laboratory, writes that A. Watson (Werribee, Victoria, Australia) has commented that the minor planet (3200) was visible in
SECCHI HI-1A images during June 17-22, noting a very short radial elongation (perpendicular to the direction of motion) that was possibly a line-of-sight
effect related to its passage through a reasonably dense, higher-speed solar outflow stream. Battams adds that the apparent brightness of
(3200) increased significantly (about 2 mag or more), peaking at mag perhaps 10-11 a few hours after perihelion (T = June 20.302 TT, q = 0.140 AU);
36 hr later, the object's had faded to magnitude roughly 13-14. Phaethon was also visible in HI-1B images during June 21-22. More formal photometry will
be performed later. [IAUC 9054, 2009 June 29]
Alan Watson recovered Phaethon in STEREO images from 2012 April 30 on May 3, noting that it seemed a little fuzzy.
Dave Jewett and Jing Li suggest Phaethon is a "rock comet". They
published a paper on the subject in The Astronomical Journal, with an an on line summary. Jewett et
al in a paper submitted to ApJL suggest that by contrast the activity seen in (596) Scheila was most likely due to impact
with a 35m diameter body.
Qicheng Zhang et al in a 2023
paper suggest that the cometary like activity is due to Sodium D
emission, a feature shared with 322P/SOHO and 323P/SOHO.
(3552) Don Quixote
Asteroid (3552) Don Quixote was discovered 30 years ago and with a period of 8.7 years has been observed at three apparitions.
It was classed as an Amor asteroid -
one that crosses the orbit of Mars, and can make moderate approaches to Jupiter (0.6 au) and the Earth (0.3 au). It appeared
anomalously bright in images taken with the Spitzer space telescope in August 2009, but only
in 2014 were the images
re-examined by researchers from the Northern Arizona University and the asteroid found to have a coma and tail.
Further images taken in 2018 March with the 4.1m Southern Astrophysical Research
Telescope at visible wavelengths also show cometary features.
Asteroid (6478) Gault was discovered in 1988 by Carolyn & Gene Shoemaker and is named after Donald Gault who was an expert in
impact cratering. It is a main-belt asteroid of the Phocaea group and has a period of 3.5 years with perihelion at 1.86 au. On 2019 January 5, observations
by ATLAS showed that it had a tail or trail, which was then found in previous images back to 2018 December 8. The imagery is consistent
with activity having started in early 2018 November, probably in a collision.
The (25) Phocaea group of asteroids are thought to be the remains of a major
collision that took place 2.2 billion years ago. A second tail was
discovered on January 26, effectively ruling out the impact hypothesis. NASA/GFC
suggest that the asteroid was spun up by the YORP effect and is now rotating too
fast to retain surface material, which is shed in the tails.
(62412) 2000 SY178 [P/LINEAR]
S. S. Sheppard, Carnegie Institution for Science, Washington and C. A. Trujillo, Gemini Observatory,
reported the detection of a faint tail to the main-belt minor planet (62412) 2000 SY178 in three 400-s VR-band
CCD exposures taken with the Blanco 4-m telescope at Cerro Tololo on 2014 March 28. The faint tail was
observed at position angle about 295 degrees and extended about 1' from the nucleus.
Follow-up observations at the Magellan telescope on May 1 and 2 confirmed the activity of (62412). [IAUC 9272, 2014 October 30]
The asteroid has a period of 5.6 years and was at perihelion at 2.9 au in 2013 March. It was discovered by LINEAR on
2000 September 28.
The SPA ENB provided additional information: A new active asteroid, numbered 62412, has
been discovered in the main asteroid belt between Mars and Jupiter. It is the first
comet-like object seen in the Hygiea family of asteroids. Active asteroids are a newly
recognized phenomenon and 62412 is only the 13th known active asteroid in the main
asteroid belt. It is estimated that there may be about 100 of them in the main asteroid
belt. Active asteroids have stable orbits between Mars and Jupiter like other asteroids;
unlike other asteroids, however, they sometimes have the appearance of comets, when dust
or gas is ejected from their surfaces, creating a sporadic tail effect. Astronomers
recently discovered a tail on 62412, an object which had been known as an ordinary
asteroid for over a decade. The reasons for the loss of material and the formation of a
tail in active asteroids are unknown, although there are several theories such as recent
impacts or sublimation from solid to gas of exposed ices.
In the past, asteroids were thought to be mostly unchanging objects, but an improved
ability to observe them has allowed scientists to discover tails and comas, the latter
being like the thin envelopes of atmosphere surrounding comets' nuclei. Discoveries such
as this one can help researchers to determine the processes that cause some asteroids to
become active. They found that 62412 has a very fast rotation that may shift surface
material, some of which may leave the surface and form the comet-like appearance. The tail
may be created directly from material ejected from the fast-rotating body, or from ice
within it subliming into water vapour after being freshly exposed on the surface. The
density of 62412 has been found to be typical of primitive asteroids and not consistent
with the much lower densities comets.
Didymos is a binary asteroid. The secondary component, Dimorphos, was targeted by the NASA DART
interceptor mission on 2022 September 27. The asteroid brightened dramatically on impact,
and susbsequently developed multiple tails.
Not numbered, but seen at two returns
P/LINEAR = 2000 XO8
An asteroid discovered by LINEAR on 2000 December 1.38 was found to show a
coma and tail in images taken by the Deep Ecliptic Patrol of
the Southern Sky (DEEP-South) team, in CCD images taken with the
Korea Microlensing Telescope Network (KMTNet) 1.6-m f/3.22 telescope at
Siding Spring Observatory (SSO) in Australia in October and the same type of telescope
installed at Cerro Tololo Interamerican Observatory (CTIO) in Chile in November.
[CBET 4460, 2017 December 13]. The comet was at perihelion at 1.5 au
in 2017 October and was previously classed as an Outer Main-belt asteroid.
It has a Jupiter MOID of 0.016 au, and will pass 0.23 au from the planet in
2042. This will be followed by an approach to the Earth at 0.33 au in
A/Lemmon = 2015 EG
This Aten type asteroid was discovered by the Mt Lemmon Survey in images taken with the 1.5m
reflector on 2015 March 9.33. At the close approach in 2019 March, radar measurements showed that
it was experiencing non-gravitational forces. [CBET 4786, 2020 May 30]. The asteroid is an NEO and PHO.
The next perihelion is at 0.6 au in 2020 July and it has the exceptionally short period of 0.8 years.
The orbit has an Earth MOID of 0.003 au and the object makes frequent close passes to both Earth and Venus.
The most recent close approach to the Earth was 0.0030 au on 2019 March 4 when it also passed 0.0031 au from the Moon,
and to Venus was 0.05 au on 2018 January 21. The next Earth approach will be to 0.036 au on 2023 March 4.
(264357) = A/LINEAR = 2000 AZ93
This Aten type asteroid was discovered by LINEAR in images taken on 2000 January 7.08. At the close approach in 2019 December, radar measurements showed that
it was experiencing non-gravitational forces. [CBET 4787, 2020 May 30]. The asteroid is an NEO and PHO.
The most recent perihelion was at 0.5 au in 2020 May and it has the exceptionally short period of 0.65 years.
The orbit has an Earth MOID of 0.022 au and the object makes frequent close passes to the Earth, Venus and Mercury.
The most recent close approach to the Earth was 0.0057 au on 2019 December 16,
and to Mercury was 0.07 au on 2017 February 15.
A/Spacewatch = 2005 XR132
This outer main-belt asteroid was discovered by Spacewatch on 2005 December 5.47.
It has perihelion at 2.1 au and a period of 7.3 years. Lulin Observatory report
in ATel 14522 [2021 April 7] that a tail was present in images taken on 2021 April 5 and 6. They suggest that
activity had begun about 100 days earlier. They do not say whether a coma was also present, so the tail
may represent an impact event. Sam Deen notes that the perihelion distance has slowly been decreasing since 1200
when it was around 3.6 au. Before then it was a quasi-Hilda type orbit.
A/WISE = 2010 LH15 = 2010 TJ 175
The WISE spacecraft discovered an object on 2010 June 3.50 and followed it until June 9. The Catalina Sky Survey
discovered an object on 2010 October 28.22, which received a designation, though pre-discovery observations by the
Survey had previously been published. There are NEAT observations from 2001 and subsequent observations to 2019. It
is classed as a Main Belt Asteroid, with a period of 4.5 years and is next at perihelion at 1.8 au in 2024 March. A
paper by Colin Chandler et al announced that it showed cometary activity on 2019 September 30 in a DECam image. Further
investigation showed cometary activity in 2010, when it was near perihelion. They suggest that it may again show
activity from late 2023.
SOHO comets of three or more returns
2008 N4 (S04P/SOHO)
Brian Marsden noted in MPEC 2008-P60 [2008 August 12]:
R. Kracht suggests that the Kracht-group comet C/2008 N4 is a return of
C/2002 S7, principally on the assumption that C/2002 S7 was itself a return
of one of C/1996 X5, C/1996 X4 or C/1996 X3 (see MPEC 2006-C49). The derived orbit
links C/2002 S7 and C/2008 N4. This gravitational
linkage leads to a previous perihelion time of T = 1996 Dec. 6.00, earlier by
a few hours than the values for the aforementioned 1996 comets.
This possibly suggests the presence of non-gravitational effects, which would
confirm the cometary nature of these objects. Further work by Brian Marsden confirmed my suggestion
and in MPEC 2009-J14 [2009 May 4] he noted:
Following up on MPEC 2008-P60,
R. Kracht has suggested that the correct linkage for C/2002 S7 = C/2008 N4 is
with C/1996 X3, on the assumption that the comet was affected by small
nongravitational forces (see also MPEC 2009-H56). The nongravitational
linkage, with parameters A1 = 0.0000, A2 = +0.0027, is based on Kracht's work.
2000 C4 (S05P/SOHO)
On 2011 July 17 Alan Watson reported a Marsden group comet in real time C3 images. Rainer Kracht computed an orbit and then
linked the object to 2000 C4 == 2005 W1. A non-gravitational parameter was required to match the perihelion dates.
S06P/SOHO = 2003 T12 = 2012 A3 = 2016 Dx
On 2012 January 19 Alan Watson discovered a fuzzy object with tail in STEREO H1b images from January 17.
William Thompson then found images in COR2B. It showed strong forward scattering brightening.
Man-To Hui (Cantonese, "Wentao Xu", "Wen-Tao Hsu" in Mandarin)
calculated a preliminary parabolic orbit and added astrometric measurements of the COR2B images. Rainer
Kracht added STEREO vectors and calculated a short period orbit, which he then linked to 2003 T12 (SOHO), which
Brian Marsden had noted might be a short period comet. He suggested that it should also be visible in STEREO images
from 2007, and Alan Watson found it in images from November that year. Rainer
notes that the comet made an approach to the Earth at 0.18 au on 2008 January
26. At the time of closest approach it was around -50 declination and
near quadrature. The comet has a period of 4.1 years, with perihelion at 0.6 au.
The IAU decided to ignore the discovery and orbit
computation sequence, which would give a designation of 2012 B1 because pre-discovery observations made earlier in January
became available, and gave the designation of 2012 B1 to a comet discovered by
PanSTARRS on January 25.
The comet was recovered by Worachate Boonplod in STEREO-A images from 2016 February
20. A linked orbit was published on March 12 [MPEC 2016-E131]
S07P/SOHO = 2002 R1 = 2008 A3 = 2013 Kx
Peiyuan Sun and Rainer Kracht discovered a Marsden group comet on 2013 May 26. They both
linked this to previous returns of a SOHO comet that had been expected to return about June 1,
so non-gravitational parameters are required.
S08P/SOHO = 2008 Y12 = 2014 K3
A non-group comet was discovered in C2 images by Rainer Kracht on
2008 December 23. In 2012, further images were found in STEREO HI-1A frames from
December 21 and 22, which lead to an improved orbit. Michal Kusiak notes
that there is a strong similarity to the orbit of the Southern Delta Aquarids,
and Rainer Kracht suggested that the comet may have a short period.
A non-group SOHO comet discovered in C2 images by Zhijian Xu on 2014 May 17 was quickly linked to 2008 Y12 by Michal Kusiak
and the orbit confirmed by Reiner Kracht. A linked orbit by Gareth Williams was published on MPEC 2014-K37 on May 24. The comet
has a period of 5.4 years and perihelion 0.07 au.
Published by Jonathan Shanklin. Jon Shanklin - email@example.com