asteroids – Cosmic Reflections

Minor Planets Named After Their Discoverers

To the best of my knowledge, only 18 minor planets have been named after their discoverers. While the discoverer has first naming rights, they cannot name a minor planet after themselves, though they can (and sometimes do) name a minor planet after a spouse, parent, or child.

Of course, many minor planet discoverers have minor planets named after them, but almost always these are discoveries by someone else who decides to name one of “their” minor planets after the other discoverer.

In the rare situation when someone decides (and has the authority) to name a discoverer’s minor planet after the discoverer, it is almost always a posthumous honor. Comet discoveries, on the other hand, are automatically named after their discoverer(s).

I have reader Rafael to thank for letting me know that Eugène Delporte does indeed have an asteroid he discovered named after him (see comments after Eugène Delporte and the Constellation Jigsaw) and this got me wondering if there were other examples. I wrote a SAS program to do some fuzzy matching between asteroid name and asteroid discoverer, and came up with the following list. Let me know if there are any others I missed, and I will include them here.

792 Metcalfia
Discovered 1907 Mar 20 by Joel Hastings Metcalf (1866-1925) at Taunton, Massachusetts.

989 Schwassmannia
Discovered 1922 Nov 18 by Arnold Schwassmann (1870-1964) at Bergedorf, Germany.

1074 Beljawskya
Discovered 1925 Jan 26 by Sergey Ivanovich Belyavskij (1883-1953) at Simeïs, Crimea.

1111 Reinmuthia
Discovered 1927 Feb 11 by Karl Reinmuth (1892-1979) at Heidelberg, Germany.

1274 Delportia
Discovered 1932 Nov 28 by Eugène J. Delporte (1882-1955) at Uccle, Belgium.

1596 Itzigsohn
Discovered 1951 Mar 8 by Miguel Itzigsohn (1908–1978) at La Plata, Argentina.

1648 Shajna
Discovered 1935 Sep 5 by Pelageya Fedorovna Shajn (1894-1956) at Simeïs, Crimea.

1655 Comas Solá
Discovered 1929 Nov 28 by José Comas Solá (1868-1937) at Barcelona, Spain.

1666 van Gent
Discovered 1930 Jul 22 by Hendrik van Gent (1899-1947) at Johannesburg, South Africa.

1777 Gehrels
Discovered 1960 Sep 24 by C. J. van Houten, I. van Houten-Groeneveld, and Tom Gehrels (1925-2011) at Palomar Mountain, California.

1927 Suvanto
Discovered 1936 Mar 18 by Rafael Suvanto (1909-1940) at Turku, Finland.

2044 Wirt
Discovered 1950 Nov 8 by Carl A. Wirtanen (1910-1990) at Mount Hamilton, California.

2246 Bowell
Discovered 1979 Dec 14 by Edward L. G. Bowell (1943-2023) at Anderson Mesa, Arizona.

3019 Kulin
Discovered 1940 Jan 7 by György Kulin (1905-1989) at Budapest, Hungary.

5540 Smirnova
Discovered 1971 Aug 30 by Tamara Mikhajlovna Smirnova (1935-2001) at Nauchnyj, Crimea.

5900 Jensen
Discovered 1986 Oct 3 by Poul B. Jensen (?-) at Brorfelde, Denmark.

19911 Rigaux
Discovered 1933 Mar 26 by Fernand Rigaux (1905-1962) at Uccle, Belgium.

96747 Crespodasilva
Discovered 1999 Aug 16 by Lucy d’Escoffier Crespo da Silva (1978-2000) at Westford, Massachusetts.

Incidentally, here are the three most prolific minor planet discoverers that still have an unnamed minor planet discovery that could be named after them. There are, of course, many others who deserve this honor.

Eleanor F. Helin (1932-2009)
Even though 3267 Glo is named after her nickname “Glo”, why not designate one of her discoveries as Helin or Eleanor Helin or Eleanorhelin? There are many still available, beginning with 5131 (1990 BG).

Carolyn Shoemaker (1929-2021)
Though 4446 Carolyn is named after her, why not designate one of her discoveries as Carolyn Shoemaker or Carolynshoemaker? There are many still available, beginning with 48576 (1994 NN₂).

Gary Hug (1950-)
There are many still available, including 32165 (1998 FS₉₂).

4534 Rimskij-Korsakov

On Sunday afternoon, October 13, 2024, I attended a wonderful concert by the Southern Arizona Symphony Orchestra (SASO) that included a rousing performance of Scheherazade by the Russian composer Nikolai Rimsky-Korsakov.

Early that evening, I was the first person in the world to observe the composer’s namesake asteroid 4534 Rimskij-Korsakov passing in front of a distant star and, briefly, blocking its light. As a classical music lover, that made me very happy.

The 0.5-second occultation of the 13.6-magnitude star UCAC4 558-003434 by the asteroid
4534 Rimskij-Korsakov on 14 Oct 2024 2:23:46 UT as seen from Tucson, Arizona
using an 8-inch telescope

4534 Rimskij-Korsakov was discovered on 6 Aug 1986 by the Russian astronomer Nikolai Chernykh (1931-2004) at the Crimean Astrophysical Observatory near the small settlement of Nauchnyi on the Crimean peninsula, part of Ukraine but illegally occupied by Putin’s Russian forces since 2014.

At the time of its discovery, this asteroid received its preliminary designation 1986 PV₄. As is the custom, the discoverer gets to choose a name for the asteroid if they so desire, and Nikolai Chernykh decided to name his discovery after Nikolai Rimsky-Korsakov (1844-1908). This name was approved by the IAU and published in Minor Planet Circular 23352 on 25 Apr 1994.

4534 Rimskij-Korsakov is not a large asteroid. Its average diameter is estimated to be just 9.9 miles. Had I been right on the centerline of the asteroid’s shadow, I should have seen the star disappear for about 1.2 seconds. Given that I had to use an integration time of 0.27^s due the faintness of the occulted star, the 0.5-second event I recorded had only two data points in the “dip” where the 13.6 magnitude star disappeared leaving only the sky background since the asteroid’s estimated magnitude was just 17.5^m. Normally, one likes to have at least three data points in the dip, but two is better than one and the event happened at exactly the predicted time.

Nikolai Rimsky-Korsakov wrote a lot of great music, and he was a master of orchestration and orchestral “colors”. Here are my favorite works. If you don’t already know them, give them a listen!

Capriccio espagnol
Le Coq d’Or, Suite [arranged by Alexander Glazunov (1865-1936) & Maximilian Steinberg (1883-1946)]
Russian Easter Festival Overture
Scheherazade
Suite from The Snow Maiden
Symphony No. 2, “Antar”
The Tale of Tsar Saltan, Suite

Superheavy Elements

There are currently 118 known chemical elements. The most recent, 118 Oganesson (chemical symbol Og), was first synthesized in 2002 . Its only known isotope, $\mathbf{\frac{294}{118}\textrm{\textbf{Og}}}$ (118 protons + 176 neutrons = 294 nucleons), has a half-life of just 0.0007 seconds, and to date only five oganesson atoms have been produced.

It is possible, given our current knowledge of nuclear physics, that there is at least one island of nuclear stability where stable or quasi-stable isotopes of superheavy elements exist. One such island might exist around Z = 164, that is an element having 164 protons and something like 246 neutrons.

Are any superheavy elements stable enough to be found in nature? Is there any astrophysical process that could produce them? If superheavy elements exist, we would expect such matter to have a mass density in excess of the densest-known stable element, osmium (element 76), 22.59 g/cm³. Superheavy elements around Z = 164 are expected to have a mass density between 36.0 and 68.4 g/cm³.

Researchers at the University of Arizona in Tucson explain that superheavy elements might exist in nature, either in the exotic form of extremely dense alpha matter — nuclear matter composed of alpha particles in a Bose-Einstein condensate-like configuration — or as standard matter. Though a long shot, they suggest looking at asteroids (and other objects) possibly having anomalously high densities, which they call Compact Ultradense Objects (CUDOs).

In order to calculate the density of an asteroid, you need to measure its volume and its mass. The volume can be calculated if you know the size and shape of the asteroid, and the mass can best be calculated if the asteroid has a satellite (either natural or artificial), or from a spacecraft flyby. A less certain mass can be calculated by measuring how an asteroid gravitationally perturbs a neighboring asteroid as they both orbit around the Sun. We must keep in mind that any asteroids that presently appear to have an unusually high density may later be found to have a more normal density upon better estimates of the size and shape of the asteroid, and especially its mass.

The most recent available table of asteroid bulk densities can be found on the SiMDA (Size, Mass, and Density of Asteroids) web site. In that table, a bulk density accuracy rank of A (most accurate) to E (least accurate), and X (unrealistic) for each object is given. Among the A-rank densities, we find that 16 Psyche is listed as having the highest bulk density of 3.90 ± 0.29 g/cm³. NASA’s Psyche robotic spacecraft was launched on October 13, 2023 and is expected to begin orbiting 16 Psyche in August 2029.

Among the B-rank densities, two asteroids have nominal bulk densities higher than 16 Psyche’s: 135 Hertha at 4.45 ± 0.63 g/cm³ and 192 Nausikaa at 4.10 ± 0.70 g/cm³.

Among the C-rank densities, 21 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "C" Asteroid Densities (> 16 Psyche)

206 Hersilia	6.08 ± 2.55
181 Eucharis	5.46 ± 2.43
410 Chloris	4.96 ± 2.41
679 Pax	4.95 ± 1.45
110 Lydia	4.88 ± 1.75
97 Klotho	4.80 ± 1.01
124 Alkeste	4.74 ± 2.22
275 Sapientia	4.69 ± 1.12
92 Undina	4.64 ± 1.75
34 Circe	4.63 ± 1.21
56 Melete	4.57 ± 1.07
102 Miriam	4.46 ± 1.88
680 Genoveva	4.37 ± 2.06
129 Antigone	4.35 ± 2.14
69 Hesperia	4.33 ± 1.11
709 Fringilla	4.12 ± 1.98
89 Julia	4.01 ± 1.61
675 Ludmilla	3.99 ± 1.94
201 Penelope	3.99 ± 1.97
455 Bruchsalia	3.93 ± 1.29
354 Eleonora	3.93 ± 1.84

Among the D-rank densities, 16 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "D" Asteroid Densities (> 16 Psyche)

250 Bettina	7.84 ± 5.42
138 Tolosa	7.69 ± 4.39
360 Carlova	6.62 ± 4.51
388 Charybdis	5.80 ± 3.66
43 Ariadne	5.54 ± 2.84
536 Merapi	5.39 ± 4.77
172 Baucis	5.34 ± 3.31
420 Bertholda	4.94 ± 4.44
103 Hera	4.78 ± 2.87
491 Carina	4.58 ± 3.11
683 Lanzia	4.49 ± 2.69
849 Ara	4.29 ± 2.18
506 Marion	4.16 ± 2.29
363 Padua	4.10 ± 2.25
705 Erminia	4.02 ± 2.39
786 Bredichina	3.91 ± 2.28

Among the E-rank densities, 7 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "E" Asteroid Densities (> 16 Psyche)

2004 PB108	6.74 ± 7.23
1013 Tombecka	6.39 ± 53.43
306 Unitas	6.23 ± 6.77
132 Aethra	5.09 ± 7.72
445 Edna	4.60 ± 4.91
147 Protogeneia	4.18 ± 5.03
769 Tatjana	4.09 ± 4.38

Among the X-rank densities, 14 asteroids have nominal bulk densities higher than 16 Psyche’s:

Rank "X" Asteroid Densities (> 16 Psyche)

1686 De Sitter	430.61 ± 213.19
33 Polyhymnia	75.32 ± 9.72
1428 Mombasa	43.03 ± 14.78
152 Atala	42.29 ± 10.80
949 Hel	12.31 ± 5.14
582 Olympia	9.98 ± 27.31
61 Danae	9.74 ± 9.45
665 Sabine	9.05 ± 5.19
217 Eudora	8.94 ± 0.64
204 Kallisto	8.89 ± 26.79
234 Barbara	8.89 ± 29.30
202 Chryseis	8.66 ± 1.63
126 Velleda	8.64 ± 106.21
67 Asia	8.59 ± 1.23

Obviously, most—if not all—of the asteroids listed above will eventually be found to have bulk densities less than that of 16 Psyche as more accurate masses and volumes are determined. Presently, only the following asteroids have minimum bulk densities greater than that of 16 Psyche, assuming the mean error listed is correct:

Asteroid Densities > 16 Psyche (within error)

1686 De Sitter	430.61 ± 213.19
33 Polyhymnia	75.32 ± 9.72
1428 Mombasa	43.03 ± 14.78
152 Atala	42.29 ± 10.80
949 Hel	12.31 ± 5.14
217 Eudora	8.94 ± 0.64
202 Chryseis	8.66 ± 1.63
67 Asia	8.59 ± 1.23

LaForge, Price, and Rafelski choose 33 Polyhymnia as the current best candidate to search for superheavy elements. Even a small amount of superheavy elements (especially in the alpha matter state) could significantly raise the bulk density of the asteroid as a whole. Kretlow lists the mass of 33 Polyhymnia as (6.20 ± 0.74) × 10¹⁸ kg and its volume-equivalent diameter as 54.0 ± 0.9 km, giving a bulk density around 75 g/cm³.

This finding is not without controversy, however. See the following discussion:

https://groups.io/g/mpml/topic/33_polyhymnia/101917502

References
Kretlow, M. Size, Mass and Density of Asteroids (SiMDA) – A Web Based Archive and Data Service” (2020). https://astro.kretlow.de/?SiMDA

LaForge, E., Price, W. & Rafelski, J. Superheavy elements and ultradense matter. Eur. Phys. J. Plus 138, 812 (2023). https://arxiv.org/abs/2306.11989
https://doi.org/10.1140/epjp/s13360-023-04454-8

Interior Asteroids

157 asteroids have orbits that lie entirely within Earth’s aphelion distance from the Sun (1.016710 AU). That number reduces to 54 inside Earth’s semimajor axis distance (1.000001 AU). That number further reduces to 28 inside Earth’s perihelion distance (0.983292 AU). Those 28 asteroids are listed below.

Only one asteroid lies entirely within Venus’s orbit, 594913 ‘Ayló’chaxnim (2020 AV₂)¹, and none are known inside Mercury’s orbit…so far. Asteroids inside of the Earth’s orbit are extremely difficult to detect since their angular distance from the Sun is never very large, and the glare of the Sun interferes. This is especially true for any asteroids that might exist inside of Mercury’s orbit.

An asteroid is given a provisional designation when it is discovered that begins with the year of discovery. After the orbit of the asteroid has been sufficiently well-determined, it is given a number. Then, eventually, the numbered asteroid is given a name.

Only 8 of the 28 asteroids entirely within Earth’s perihelion distance have received numbers, and only two of these have been given a name: ‘Ayló’chaxnim and Atira.

Interestingly, half of these 28 asteroids have been discovered since 2017, including 1 so far this year. The first was discovered in 1998.

In the table below, i is the orbital inclination relative to the ecliptic plane, e is the orbital eccentricity, q is the perihelion distance, a is the semimajor axis distance, Q is the aphelion distance, and P is the orbital period. The table is listed in order of aphelion distance, smallest to largest.

Asteroids with orbits that lie entirely within Earth’s perihelion distance from the Sun

¹pronunciation: ai-LOH-chakh-nym

Reference

IAU Minor Planet Center

We are the official body that deals with astrometric observations and orbits of minor planets (asteroids) and comets.

Asteroids: Take a Number

Italian monk, mathematician, and astronomer Giuseppe Piazzi (1746-1826) discovered an unexpected 8th magnitude object in Taurus near Mars and the Pleiades at around 8:00 p.m. on January 1, 1801 at his observatory in Palermo, Sicily. Thinking it a comet, he recorded the position of the object over several nights, until illness forced him to quit on February 11, just a few days after the object passed fairly close to Mars. By early May, the object was too close to the Sun in the western sky to observe, and Piazzi despaired of ever recovering the object. The now-famous 24-year-old German mathematician Carl Gauss (1777-1855) came to the rescue. Gauss used Piazzi’s positions to determine an orbit for Ceres (so named by Piazzi) and predicted from the scant data its future positions when it would once again be visible in the night sky. Ceres was recovered only a half-degree away from its predicted position by Hungarian astronomer Franz Xaver von Zach (1754-1832) on December 7, close to Denebola and not far from a close conjunction of the planets Jupiter and Saturn, and then confirmed after a long stretch of cloudy weather on December 31, 1801. The German amateur astronomer Heinrich Olbers (1758-1840) found Ceres at Bremen two days later on January 2, 1802. Olbers (of Olbers’ Paradox fame) discovered the second asteroid, Pallas, on March 28, 1802. Many, many more asteroids have been discovered since then. They are sequentially numbered, originally in order of their discovery date, but nowadays in order of their receiving a precise orbit determination.

Fast forward.

The names of asteroids 998 through 1002, discovered between August 6-15, 1923, have special significance.

998 Bodea – named in honor of German astronomer Johann Elert Bode (1747-1826), whose empirical relationship of the distances of the planets (Titius-Bode Law) indicated that there should be a planet between the orbits of Mars and Jupiter, touching off a massive search led by von Zach for a new planet.

999 Zachia – named in honor of Franz Xaver von Zach, who published Piazzi’s observations and recovered Ceres after Gauss’ predicted positions.

1000 Piazzia – named in honor of Giuseppe Piazzi, who discovered the first asteroid, 1 Ceres.

1001 Gaussia – named in honor of Carl Friedrich Gauss, who predicted the position of Ceres so it could be recovered.

1002 Olbersia – named in honor of Heinrich Olbers who was the second person to recover Ceres and the discoverer of the second asteroid, 2 Pallas (and 4 Vesta, by the way).

Fortunately, German astronomer Johann Daniel Titius (1729-1796) finally did get an asteroid named after him as well: 1998 Titius, discovered on February 24, 1938.

As of August 19, 2019, 796,422 minor planets (asteroids, trans-Neptunian objects, etc., but not including comets) have been discovered, but only 541,128 have orbits that are well-enough determined that they have been given a minor planet number. When a minor planet is first discovered, it is given a provisional designation based on the date of discovery. For example, 2019 PE₃ was discovered during the first half of August 2019. After enough high-quality astrometric data has been collected to determine an accurate orbit, the minor planet is assigned a number. For example, minor planet 1996 TB₁ was discovered by IOTA member George Viscome on October 5, 1996. It received a number, 35283, in 2000, and it received a name, Bradtimerson, earlier this year (2019). George submitted the name to the IAU after Brad Timerson, mentor and inspiration to many of the current crop of asteroid occultation observers, passed away on October 17, 2018. So we now have 35283 Bradtimerson.

The counts in the paragraph above show us that 67.9% of the minor planets that have been discovered have been assigned a number. Of these, only 21,922 (4.1%) have received a name.

Many asteroids have been given interesting or unusual names. Excluding the many fine individuals (real, not fictional) who have an asteroid named after them, here are a few of my favorites. There are a few here that are actually named after a person, but the minor planet name has a meaning beyond just the person’s name.

Remember, these are real places that will be visited someday. Oh, to be so lucky!

Lots of asteroids are awaiting names. Can you come up with some interesting, entertaining, or poetic ones? Give it a try, check this list or do a search here to make sure it is new, and then post a comment here and I’ll probably include your ideas in this article, giving you credit, of course. Be creative!

To get you in the spirit, here are a few names I’ve come up with:

Botanica
Distantia
Eternium
Gandalf
Hello & Goodbye [consecutive numbers, in celebration of The Beatles song written by Paul McCartney]
Luminaria
Morethanamote
Portentia
Symphonica

Have fun!

Retrograde Asteroids and TNOs

Of the 793,918 asteroids and trans-Neptunian objects (TNOs) currently catalogued, only 98 are in retrograde orbits around the Sun. That’s just 0.01%.

By “retrograde” we mean that the object orbits the Sun in the opposite sense of all the major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. From a vantage point above the north pole of the Earth, all of the major planets orbit in a counterclockwise direction around the Sun.

Source: https://community.dur.ac.uk/john.lucey/users/inner.html

But a retrograde object would be seen to orbit in a clockwise direction around the Sun, as is shown in the animation below for Jupiter retrograde co-orbital asteroid 514107 (2015 BZ₅₀₉), with respect to Jupiter and its two “clouds” of trojan asteroids.

Source: https://www.sciencenews.org/article/asteroid-jupiters-orbit-goes-its-own-way

Of these 98 retrograde objects, only 14 have orbits well-enough determined to have received a minor planet number, and only one has yet received an official name (20461 Dioretsa).

Semimajor Axis (a) between…	Number of Retrograde Minor Planets
Mars – Jupiter	3
Jupiter – Saturn*	20
Saturn – Uranus*	15
Uranus – Neptune*	20
TNOs	40

*asteroids between the orbits of Jupiter and Neptune are often referred to as centaurs

At least some of these objects may be captured interstellar objects.

Let’s now take a look at some of these 98 retrograde objects in greater detail.

20461 Dioretsa
The first retrograde asteroid to be discovered was 20461 Dioretsa, in 1999. The only named retrograde asteroid to date, Dioretsa is an anadrome of the word “asteroid”. It is a centaur in a highly eccentric orbit (0.90), ranging between the orbits of Mars and Jupiter out to beyond the orbit of Neptune. Objects in cometlike orbits that show no evidence of cometary activity are often referred to as damocloids. Dioretsa is both a centaur and a damocloid. Its orbital inclination (relative to the ecliptic) is 160°, which is a 20° tilt from an anti-ecliptic orbit. It takes nearly 117 years to orbit the Sun once. It is a dark object with a reflectivity only around 3% and is estimated to be about 9 miles across.

2010 EQ₁₆₉
This retrograde asteroid holds the distinction (at least temporarily) of being the most highly-inclined main-belt asteroid (91.6°), relative to the ecliptic plane. It is also the retrograde asteroid with the smallest semimajor axis (2.05 AU) and lowest orbital eccentricity (0.10). Unfortunately, it was discovered after the fact by analyzing past data from the Wide-field Infrared Survey Explorer (WISE) space telescope, and has not been seen since. We have only a three-day arc of 17 astrometric observations of 2010 EQ₁₆₉between March 7-9, 2010 from which to determine its orbit. Nominally, 2010 EQ₁₆₉ orbits the Sun at nearly a right angle to the ecliptic plane once every 2.9 years, between the orbits of Mars and Jupiter. However, our knowledge of its orbit is extremely uncertain, as shown below, and it has been lost. Our only hope will be to back-calculate the positions of future asteroids discovered to these dates to see if it matches the WISE positions.

Element	Value	1σ Uncertainty
Inclination (i)	91.606°	18.177°
Semimajor Axis (a)	2.0518 AU	2.2176
Orbital Eccentricity (e)	0.10153	0.90213
Orbital Period (P)	2.94^y	4.765

2013 BL₇₆
This retrograde TNO has the largest known semi-major axis of any of the retrograde non-cometary objects: 966.4274 ± 2.2149 AU. In a highly eccentric cometlike orbit (e = 0.99135), its perihelion is in the realm of the centaurs between the orbits of Jupiter and Saturn (8.35 AU), and its aphelion is way out around 1,924 AU. It takes about 30,000 years to orbit the Sun. Its orbit is inclined 98.6° with respect to the ecliptic.

2013 LA₂
This retrograde centaur is in an orbit closest to the ecliptic plane (i = 175.2°), tilted 4.8° with respect to the ecliptic. It orbits the Sun about once every 21 years between the orbits of Mars and Uranus.

2017 UX₅₁
The distinction for this retrograde TNO is that it has the highest orbital eccentricity of any non-cometary solar system object (e = 0.9967). Or is it an old inactive comet? 2017 UX₅₁ orbits the Sun every 7,419 ± 2,883 years as close in as between the orbits of Earth and Mars (perihelion q = 1.24 AU)—classifying it as an Amor object—out to far beyond the orbit of Neptune (aphelion Q = 759.54 ± 196.77 AU). Its orbital inclination is 108.2°.

343158 (2009 HC₈₂)
An Apollo asteroid, 343158 is the only known retrograde near-Earth asteroid (NEA), with an orbital inclination of 154.4°. It orbits the Sun every 4.0 years, between 0.49 AU (almost as close in as the aphelion of Mercury) out to 4.57 AU (between the orbits of Mars and Jupiter).

References
Conover, E., 2017. Science News, 191, 9, 5.

JPL Small-Body Database Browser, https://ssd.jpl.nasa.gov/sbdb.cgi, retrieved 31 March 2019.

Kankiewicz, P., Włodarczyk, I., 2018. Planetary and Space Science, 154, 72-76.

Minor Planet Center, https://minorplanetcenter.net/iau/MPCORB.html, retrieved 28 March 2019.

Namouni F., Morais M. H. M., 2018. MNRAS, 477, L117.

Wiegert, P., Connors, M., Veillet, C., 2017. Nature, 543, 687–689.

Turnkey System for Occultations

Finally, a turnkey system is available for recording stellar occultations by asteroids and trans-Neptunian objects (TNOs)! All you need besides the kit is a telescope and a PC. A big thank you to Ted Blank and IOTA for putting this together!

Occultation Recording Kit

Highly sensitive RunCam Night Eagle Astro Edition video camera
0.5x focal reducer & adapters to attach camera to 1¼-inch eyepiece holder
IOTA VTI (Video Time Inserter) V3
StarTech SVID2USB23 USB video capture device
Instruction manual
Cost: $518

https://occultations.org/observing/recommended-equipment/iota-vti/

We need more observers in the Midwest (everywhere, really) to give us more chords across the asteroids and TNOs, thus increasing the scientific value of the observations. Right now, we are desperately in need of observers in Iowa (where I lived for many years and will always be home to me), and we have precious few active observers in Wisconsin (yours truly), Minnesota (Steve Messner), and Illinois (Bob Dunford, Aart Olsen, Randy Trank).

If you have an interest in pursuing this interesting and rewarding speciality that gives you the opportunity to make a valuable scientific contribution, feel free to post a comment here and I’ll be happy to help!

Direct Imaging of Exoplanets Through Occultations

Planetary orbits are randomly oriented throughout our galaxy. The probability that an exoplanet’s orbit will be fortuitously aligned to allow that exoplanet to transit across the face of its parent star depends upon the radius of the star, the radius of the planet, and the distance of the planet from the star. In general, planets orbiting close-in are more likely to be seen transiting their star then planets orbiting further out.

The equation for the probability of observing a exoplanet transit event is

$p_{tra} = \left (\frac{R_{\bigstar}+R_{p}}{a} \right )\left (\frac{1}{1-e^{2}} \right )$

where p_tra is the transit probability, R_* is the radius of the star, R_p is the radius of the planet, a is the semi-major axis of the planetary orbit, and e is the eccentricity of the planetary orbit

Utilizing the data in the NASA Exoplanet Archive for the 1,463 confirmed exoplanets where the above data is available (and assuming e = 0 when eccentricity is unavailable), we find that the median exoplanet transit probability is 0.0542. This means that, on average, 1 out of every 18 planetary systems will be favorably aligned to allow us to observe transits. However, keep in mind that our present sample of exoplanets is heavily biased towards large exoplanets orbiting close to their parent star. Considering a hypothetical sample of Earth-sized planets orbiting 1 AU from a Sun-sized star, the transit probability drops to 0.00469, which means that we would be able to detect only about 1 out of every 213 Earth-Sun analogs using the transit method.

How might we detect some of the other 99.5%? My admired colleague in England, Abdul Ahad, has written a paper about his intriguing idea: “Detecting Habitable Exoplanets During Asteroidal Occultations”. Abdul’s idea in a nutshell is to image the immediate environment around nearby stars while they are being occulted by asteroids or trans-Neptunian objects (TNOs) in order to detect planets orbiting around them. While there are many challenges (infrequency of observable events, narrow shadow path on the Earth’s surface, necessarily short exposure times, and extremely faint planetary magnitudes), I believe that his idea has merit and will one day soon be used to discover and characterize exoplanets orbiting nearby stars.

Ahad notes that the apparent visual magnitude of any given exoplanet will be directly proportional to the apparent visual magnitude of its parent star, since exoplanets shine by reflected light. Not only that, Earth-sized and Earth-like planets orbiting in the habitable zone of any star would shine by reflected light of the same intrinsic brightness, regardless of the brightness of the parent star. He also notes that the nearer the star is to us, the greater will be a given exoplanet’s angular distance from the occulted star. Thus, given both of these considerations (bright parent star + nearby parent star = increased likelihood of detection), nearby bright stars such as Alpha Centauri A & B, Sirius A, Procyon A, Altair, Vega, and Fomalhaut offer the best chance of exoplanet detection using this technique.

Since an exoplanet will be easiest to detect when it is at its greatest angular distance from its parent star, we will be seeing only about 50% of its total reflected light. An Earth analog orbiting Alpha Centauri A would thus shine at visual magnitude +23.7 at 0.94″ angular distance, and for Alpha Centauri B the values would be +24.9 and 0.55″.

Other considerations include the advantage of an extremely faint occulting solar system object (making it easier to detect faint exoplanets during the occultation event), and the signal boost offered by observing in the infrared, since exoplanets will be brightest at these wavelengths.

A distant (and therefore slow-moving) TNO would be ideal, but the angular size of the TNO needs to be larger than the angular size of the occulted star. However, slow-moving objects mean that occultation events will be rare.

The best chance of making this a usable technique for exoplanet discovery would be a space-based observatory that could be positioned at the center of the predicted shadow and would be able to move along with the shadow to increase exposure times (Ahad, personal communication). It would be an interesting challenge in orbital mechanics to design the optimal base orbit for such a spacecraft. The spacecraft orbit would be adjusted to match the position and velocity of the occultation shadow for each event using an ion drive or some other electric propulsion system.

One final thought on the imaging necessary to detect exoplanets using this technique. With a traditional CCD you would need to begin and end the exoplanet imaging exposure(s) only while the parent star is being occulted. This would not be easy to do, and would require two telescopes – one for the occultation event detection and one for the exoplanet imaging. A better approach would be to use a Geiger-mode avalanche photodiode (APD). Here’s a description of the device captured in 2016 on the MIT Lincoln Labs Advanced Imager Technology website:

A Geiger-mode avalanche photodiode (APD), on the other hand, can be used to build an all-digital pixel in which the arrival of each photon triggers a discrete electrical pulse. The photons are counted digitally within the pixel circuit, and the readout process is therefore noise-free. At low light levels, there is still noise in the image because photons arrive at random times so that the number of photon detection events during an exposure time has statistical variation. This noise is known as shot noise. One advantage of a pixel that can digitally count photons is that if shot noise is the only noise source, the image quality will be the best allowed by the laws of physics. Another advantage of an array of photon counting pixels is that, because of its noiseless readout, there is no penalty associated with reading the imager out frequently. If one reads out a thousand 1-ms exposures of a static scene and digitally adds them, one gets the same image quality as a single 1-s exposure. This would not be the case with a conventional imager that adds noise each time it is read out.

References
Ahad, A., “Detecting Habitable Exoplanets During Asteroidal Occultations”, International Journal of Scientific and Innovative Mathematical Research, Vol. 6(9), 25-30 (2018).
MIT Lincoln Labs, Advanced Imager Technology, https://www.ll.mit.edu/mission/electronics/ait/single-photon-sensitive-imagers/passive-photon-counting.html. Retrieved March 17, 2016.
NASA Exoplanet Archive https://exoplanetarchive.ipac.caltech.edu.
Winn, J.N., “Exoplanet Transits and Occultations,” in Exoplanets, ed. Seager, S., University of Arizona Press, Tucson (2011).

29769 (1999 CE28)

Early in the morning of Tuesday, May 29, 2018, I was fortunate enough to record a 3.2 second occultation of the 12.6 magnitude star UCAC4 359-140328 in Sagittarius by the unnamed asteroid 29769, originally given the provisional designation 1999 CE₂₈.

Not only is this the first time this asteroid has been observed to pass in front of a star, it is the smallest asteroid I have ever observed passing in front of a star. At an estimated diameter of 14.7 miles, had I been located just 7.4 miles either side of the centerline of the shadow path, I would have missed this event altogether! This is also the first positive event I’ve recorded for an (as yet) unnamed asteroid, and the first positive event I’ve recorded for an asteroid having more than a four-digit number (29769).

As you can see in the map above, the predicted shadow path was quite a ways northwest of my location. Even though I used the Gaia DR2 position for UCAC4 359-140328 for the path prediction, the existing orbital elements for asteroid 29769 did not yield a correspondingly accurate position for the asteroid.

Though a single chord across an asteroid does not give us any definitive information about its overall size and shape, it does give us a very accurate astrometric position that will be used to improve the orbital elements for this asteroid.

The central moment of this occultation event was 6:00:02.414 UT on May 29, 2018, which was about 20 seconds later than predicted. The astrometric equatorial coordinates for the star UCAC4 359-140328 referenced to the J2000 equinox (using Gaia DR2 with proper motion applied) are

UCAC4 359-140328

α = 18^h 21^m 01.6467^s

δ = -18° 20′ 46.282″

Using JPL Horizons (with the extra precision option selected), the astrometric equatorial coordinates for the asteroid 29769 (1999 CE₂₈), again referenced to the J2000 equinox, are

29769 (1999 CE₂₈)

α = 18^h 21^m 01.6388^s

δ = -18° 20′ 46.320″

As we can see above, the actual position of the asteroid at the time of the event was 0.0079 seconds of time east and 0.038 seconds of arc north of its predicted position. This observation will provide a high quality astrometric data point for the asteroid that will be used to improve its orbit. Gratifying!

As of this writing, there are 523,584 minor planets that have sufficiently well enough determined orbits to have received a number. Of these, only 21,348 have received names (4.1%). So, I guess you could say there is quite a backlog of numbered asteroids awaiting to receive names. The IAU should consider naming some minor planets after the most productive asteroid occultation observers around the world. There aren’t very many of us, and this would certainly be an encouragement to new and existing observers.

Satellite (and Meteor ) Crossings 2017-2018

Edmund Weiss (1837-1917) and many astronomers since have called asteroids “vermin of the sky”, but since October 4, 1957 another “species” of sky vermin made their debut: artificial satellites. In the process of video recording stars for possible asteroid occultations, I frequently see satellites passing through my ~¼° field of view.

I’ve put together a video montage of satellites I’ve recorded between June 21, 2017 and October 20, 2017. The component events are presented chronologically as follows:

UT Date
6-21-2017
8-15-2017
9-4-2017
9-5-2017
9-12-2017
10-20-2017 (2 satellites)

Target Star
Tycho 5723-663-1
Tycho 1668-1258-1
Tycho 1281-225-1
UCAC4 553-20591
Tycho 5731-996-1
Tycho 6289-1504-1

Asteroid
798 Ruth
30981(1995 SJ₄)
34532 (2000 SO₂₁₃)
1294 Antwerpia
85985 (1999 JW)
25036 Elizabethof

You’ll notice that sometimes the satellite crosses the field as a moving “dash”. That’s because sometimes I used longer exposure times to record a fainter target star.

In general, the slower the satellite is moving across the field, the higher is its orbit around the Earth. One must also consider how much of the satellite’s orbital motion is along your line of sight to the satellite. In the following video clip, you’ll see a slow-moving “tumbler” satellite moving from right to left across the top of the field.

UT Date
8-25-2017

Target Star
Tycho 676-828-1

Asteroid
179462 (2002 AJ₂₀₂)

On January 10th of this year, I figured out how to identify satellites crossing the telescope field of view using the amazing program Guide 9.1, which I use for all my observatory research work. On March 4th, I was hoping to be the first to record the asteroid 3706 Sinnott passing in front of a star. This asteroid is named after Sky & Telescope Senior Editor Roger Sinnott, whom I had the good fortune to work with in writing the article “A Roll-Down-Roof Observatory” in the May 1993 issue of Sky & Telescope, p. 90. Roger is amazing. He took an article that I had written and edited it in a way that only lightly touched my original text yet ended up saying what I wanted to say even better than I was able to say it myself. The mark of a great editor! Anyway, I’m sure Roger remembers me and I was looking forward to giving him the news that I had observed the first stellar occultation by “his” asteroid. Alas, it was not to be, because, as so often happens, the too-faint-to-be-seen asteroid passed either above or below the target star. The consolation prize, however, was recording a third stage Long March Chinese rocket booster (CZ-3B R/B; NORAD 43004U; International # 17069D) passing through the field. This rocket launched on November 5, 2017, and added two satellites to China’s Beidou positioning network. As you can see in the light curve below, the rotation period of the rocket booster is a bit longer than the 19 seconds of usable video I had.

UT Date
3-4-2018

Target Star
UCAC4 556-42881

Asteroid
3706 Sinnott

Once in a great while, I record a telescopic meteor. Here are two.

UT Date
7-15-2017
3-4-2018

Target Star
Tycho 6269-2747-1
UCAC4 561-14746

Asteroid
17136(1999 JE₈₂)
6890 Savinykh

References
Hughes, D. W. & Marsden, B. G. 2007, J. Astron. Hist. Heritage, 10, 21