<p>Actually, <strong>the very first binary asteroid was discovered by stellar occultation in 1980.</strong>  The evidence was rejected by the IAU, and <a href="https://en.wikipedia.org/wiki/Binary_asteroid" rel="nofollow noreferrer">wikipedia</a> credits the first binary asteroid discovery to the Galileo spacecraft finding the moon of 243 Ida in 1993.</p>
<p>The first moon of the well known asteroid <a href="https://en.wikipedia.org/wiki/216_Kleopatra" rel="nofollow noreferrer">216 Kleopatra</a> was observed through stellar occultation in 1980.  From this <a href="https://skyandtelescope.org/astronomy-news/seeing-double-30-years-later/" rel="nofollow noreferrer">article</a>:</p>
<blockquote>
<p>As occultation czar David Dunham would later report in Sky &amp;
Telescope, nine different observing stations visually timed blinkouts
of the 9th-magnitude star SAO 128066. Collectively these timings
traced chords across an irregular, elongated silhouette measuring
roughly 60 by 80 miles (95 by 130 km). &quot;But there was an unexpected
secondary occultation too!&quot; Dunham wrote. &quot;Gerald Rattley and Bill
Cooke, observing from sites 2,000 feet apart near Loma Prieta,
California, independently and nearly simultaneously saw the star
disappear for about one second.&quot;</p>
</blockquote>
<p>Dunham concluded that they had discovered a satellite of 216 Kleopatra. At that time, however, it was unknown if asteroids had satellites, and their evidence was not accepted.  There was some stigma associated with the occultation methods.   In 2008, the Keck II telescope finally verified the moons of 216 Kleopatra:</p>
<p><a href="https://i.sstatic.net/yvMTG.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/yvMTG.jpg" alt="enter image description here" /></a></p>
<p>In 2011, one of Kleopatra's moon's size and orbit was shown to be consistent with the original 1980 occultation observations, referenced in this <a href="https://arxiv.org/ftp/arxiv/papers/1310/1310.3220.pdf" rel="nofollow noreferrer">paper</a>, and reconstructed here with the original chords:</p>
<p><a href="https://i.sstatic.net/lsPrp.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/lsPrp.jpg" alt="enter image description here" /></a></p>
<p>Even though there were two independent chords that occulted the star, the IAU's former Minor Planet Director Center called the evidence &quot;shoddy&quot;, even decades later.  In 1980, he had refused to accept that asteroidal satellites existed.</p>
<p>Interestingly, even after vindication 30 years later, stellar occultation evidence for binary asteroid systems are still met with skepticism.  For example, the wikipedia page for the asteroid <a href="https://en.wikipedia.org/wiki/911_Agamemnon" rel="nofollow noreferrer">911 Agamemnon</a> says a 2012 occultation is merely 'suggestive' of the Asteroid having a satellite.  To me, the stellar occultation of the light intensity measurements from this <a href="https://arxiv.org/ftp/arxiv/papers/1310/1310.3220.pdf" rel="nofollow noreferrer">paper</a>, is far more than just suggestive, but instead clear evidence of a satellite of 911 Agamemnon:</p>
<p><a href="https://i.sstatic.net/CJ6TK.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/CJ6TK.png" alt="enter image description here" /></a></p>
<p>The large steady dip is the main body of the asteroid passing over the V magnitude 8.0 star HIP 41337 = SAO 60804 = BD= +37° 1857 = HD 70920, spectral type K0.  The small dip is the satellite passing over the star.</p>
<p><strong>Note:</strong>
It's strange to me that the discovery of binary asteroid systems is met with skepticism since the method is essentially the same method often used to detect extra-solar planets (the transit method explained nicely in this <a href="https://astronomy.stackexchange.com/questions/8605/if-alpha-centauri-as-solar-system-exactly-mirrored-our-own-what-would-we-be-ab/8628?r=SearchResults&amp;s=6%7C0.0000#8628">answer</a>).</p>

CC BY-SA 4.0
2020-12-09T03:42:51.220Z
Wow, what an amazing story! Slightly related: [Who first reported the Crab pulsar's pulsing but was dismissed by an astronomer?](https://hsm.stackexchange.com/q/11298/3869) Hmm, *Loma Prieta* sounds familliar, I was in an earthquake of the same name. In 1980 I think amateur astronomers timing occultations in the field had to either use visual timing or invest in and battery-power a photomultiplier tube and a tape recorder in order to record time resolved photometry, IAU should not have rejected the observation.
uhoh
CC BY-SA 4.0
2020-12-09T04:15:39.810Z
@uhoh There sure are a lot of cases in math and science where a discovery actually happened much earlier than the attributed date by someone other than the attributed discoverer.  I would be quite curious what the timing method and video method was used in 1980.  The 2012 Agamemnon occultation observations employed these systems: http://scottysmightymini.com/ .  I bet some similar systems were used for Arrokoth.
Connor Garcia
CC BY-SA 4.0
2020-12-09T05:12:25.430Z
Yes indeed. That's a great question and I have a hunch that its asking will be forthcoming...
uhoh
CC BY-SA 4.0
2020-12-09T03:31:52.787Z
2020-12-09T03:31:52.787Z
Connor Garcia
<p>The asteroid <a href="https://en.wikipedia.org/wiki/486958_Arrokoth" rel="nofollow noreferrer">486958 Arrokoth</a> was discovered to be binary by astronomers lugging a bunch of telescopes around (I think) camping with them. The timing offered additional astrometry for the orbit determination before New Horizon's flyby, and it also served to put an upper limit on any dust or debris cloud around the object that might suggest a farther flyby distance be considered.</p>

<p>Their hard work certainly paid off and an outline of the object was reconstructed, showing that it was likely a binary; two circular objects. This posed a bit of a mystery because there wasn't any periodic variation in brightness detected that would suggest rotation, but that's a different story.</p>

<p>Is this the only solar system object that was discovered to be binary (or higher) via occultation?</p>

<hr>

<p><a href="https://i.sstatic.net/ECNwm.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ECNwm.jpg" alt="enter image description here"></a></p>

<p><strong>above:</strong> reconstructed occultation timing from several nearby sites from <a href="https://space.stackexchange.com/a/29882/12102">this answer</a> <strong>below:</strong> series of images from New Horizons during flyby from <a href="https://space.stackexchange.com/q/34099/12102">this question</a></p>

<p>1.3 MB GIF: <a href="https://i.sstatic.net/Ci213.gif" rel="nofollow noreferrer">https://i.sstatic.net/Ci213.gif</a> also viewable in <a href="https://youtu.be/6i6K6kUOgxY" rel="nofollow noreferrer">YouTube</a></p>

CC BY-SA 4.0
2020-03-10T16:09:47.453Z
I'd suggested removing the animation.  It does little for the question and it's a megabyte in size, which is a bit rough for people without good internet connections (and lots of people still have poor internet bandwidth).
StephenG - Help Ukraine
CC BY-SA 4.0
2020-03-10T16:14:49.083Z
@StephenG okay doing so now.
uhoh
CC BY-SA 4.0
2020-03-10T17:40:33.230Z
[Buie et al. 2020](https://ui.adsabs.harvard.edu/abs/2020AJ....159..130B/abstract) give lots of detail on the Arrokoth campaign but don't say much about other targets.
Mike G
CC BY-SA 4.0
2020-03-10T23:43:46.713Z
@MikeG Thanks! It's quite a thorough write-up. I'm sure there haven't been very many campaigns involving such a choreographed deployment of portable telescopes, but it's possible a photometric "double-dip" seen from one fixed location in the same way that [Neptune's rings were first detected](https://en.wikipedia.org/wiki/Rings_of_Neptune#Discovery_and_observations) in 1968 (thought not appreciated at the time). For the purposes of this question ring discovery won't count towards the object being "binary".
uhoh
CC BY-SA 4.0
2020-03-12T11:10:47.583Z
Presumably not the only one, but KBO occultations are a fairly new trick only possible thanks to the Gaia DRs.
AtmosphericPrisonEscape
CC BY-SA 4.0
2020-06-30T01:30:51.363Z
How are you defining “binary” here?   All evidence that I’ve seen is that the two lobes of that object are in contact with each other, i.e. it’s a single object.
Eric Jensen
CC BY-SA 4.0
2020-06-30T06:43:20.070Z
@ELNJ let's adhere to standard conventions; they can be either [contact binaries](https://en.wikipedia.org/wiki/Contact_binary_(small_Solar_System_body)) like this one, or "[regular binaries](https://en.wikipedia.org/wiki/Binary_asteroid)" if you will.
uhoh
<observational-astronomy><asteroids><photometry><occultation>
Is 486958 Arrokoth (2014 MU69 aka Ultima Thule) the only solar-system object determined to be binary by occultation?
uhoh
# Is 486958 Arrokoth (2014 MU69 aka Ultima Thule) the only solar-system object determined to be binary by occultation?

(Asked by: username_0 on 2020-03-10)

The asteroid [486958 Arrokoth](https://en.wikipedia.org/wiki/486958_Arrokoth) was discovered to be binary by astronomers lugging a bunch of telescopes around (I think) camping with them. The timing offered additional astrometry for the orbit determination before New Horizon's flyby, and it also served to put an upper limit on any dust or debris cloud around the object that might suggest a farther flyby distance be considered.

Their hard work certainly paid off and an outline of the object was reconstructed, showing that it was likely a binary; two circular objects. This posed a bit of a mystery because there wasn't any periodic variation in brightness detected that would suggest rotation, but that's a different story.

Is this the only solar system object that was discovered to be binary (or higher) via occultation?

---

[![enter image description here](https://i.sstatic.net/ECNwm.jpg)](https://i.sstatic.net/ECNwm.jpg)

**above:** reconstructed occultation timing from several nearby sites from [this answer](https://space.stackexchange.com/a/29882/12102) **below:** series of images from New Horizons during flyby from [this question](https://space.stackexchange.com/q/34099/12102)

1.3 MB GIF: <https://i.sstatic.net/Ci213.gif> also viewable in [YouTube](https://youtu.be/6i6K6kUOgxY)

**Tags:** observational-astronomy, asteroids, photometry, occultation

> **Comments:**
> **username_1**: I'd suggested removing the animation.  It does little for the question and it's a megabyte in size, which is a bit rough for people without good internet connections (and lots of people still have poor internet bandwidth).  
> **username_0**: @StephenG okay doing so now.  
> **username_2**: [Buie et al. 2020](https://ui.adsabs.harvard.edu/abs/2020AJ....159..130B/abstract) give lots of detail on the Arrokoth campaign but don't say much about other targets.  
> **username_0**: @MikeG Thanks! It's quite a thorough write-up. I'm sure there haven't been very many campaigns involving such a choreographed deployment of portable telescopes, but it's possible a photometric "double-dip" seen from one fixed location in the same way that [Neptune's rings were first detected](https://en.wikipedia.org/wiki/Rings_of_Neptune#Discovery_and_observations) in 1968 (thought not appreciated at the time). For the purposes of this question ring discovery won't count towards the object being "binary".  
> **username_3**: Presumably not the only one, but KBO occultations are a fairly new trick only possible thanks to the Gaia DRs.  
> **username_4**: How are you defining “binary” here?   All evidence that I’ve seen is that the two lobes of that object are in contact with each other, i.e. it’s a single object.  
> **username_0**: @ELNJ let's adhere to standard conventions; they can be either [contact binaries](https://en.wikipedia.org/wiki/Contact_binary_(small_Solar_System_body)) like this one, or "[regular binaries](https://en.wikipedia.org/wiki/Binary_asteroid)" if you will.  

---

## 1 answers

### Answer by username_5 on 2020-12-09. Score: 4 | Accepted answer

Actually, **the very first binary asteroid was discovered by stellar occultation in 1980.** The evidence was rejected by the IAU, and [wikipedia](https://en.wikipedia.org/wiki/Binary_asteroid) credits the first binary asteroid discovery to the Galileo spacecraft finding the moon of 243 Ida in 1993.

The first moon of the well known asteroid [216 Kleopatra](https://en.wikipedia.org/wiki/216_Kleopatra) was observed through stellar occultation in 1980. From this [article](https://skyandtelescope.org/astronomy-news/seeing-double-30-years-later/):

> As occultation czar David Dunham would later report in Sky &
> Telescope, nine different observing stations visually timed blinkouts
> of the 9th-magnitude star SAO 128066. Collectively these timings
> traced chords across an irregular, elongated silhouette measuring
> roughly 60 by 80 miles (95 by 130 km). "But there was an unexpected
> secondary occultation too!" Dunham wrote. "Gerald Rattley and Bill
> Cooke, observing from sites 2,000 feet apart near Loma Prieta,
> California, independently and nearly simultaneously saw the star
> disappear for about one second."

Dunham concluded that they had discovered a satellite of 216 Kleopatra. At that time, however, it was unknown if asteroids had satellites, and their evidence was not accepted. There was some stigma associated with the occultation methods. In 2008, the Keck II telescope finally verified the moons of 216 Kleopatra:

[![enter image description here](https://i.sstatic.net/yvMTG.jpg)](https://i.sstatic.net/yvMTG.jpg)

In 2011, one of Kleopatra's moon's size and orbit was shown to be consistent with the original 1980 occultation observations, referenced in this [paper](https://arxiv.org/ftp/arxiv/papers/1310/1310.3220.pdf), and reconstructed here with the original chords:

[![enter image description here](https://i.sstatic.net/lsPrp.jpg)](https://i.sstatic.net/lsPrp.jpg)

Even though there were two independent chords that occulted the star, the IAU's former Minor Planet Director Center called the evidence "shoddy", even decades later. In 1980, he had refused to accept that asteroidal satellites existed.

Interestingly, even after vindication 30 years later, stellar occultation evidence for binary asteroid systems are still met with skepticism. For example, the wikipedia page for the asteroid [911 Agamemnon](https://en.wikipedia.org/wiki/911_Agamemnon) says a 2012 occultation is merely 'suggestive' of the Asteroid having a satellite. To me, the stellar occultation of the light intensity measurements from this [paper](https://arxiv.org/ftp/arxiv/papers/1310/1310.3220.pdf), is far more than just suggestive, but instead clear evidence of a satellite of 911 Agamemnon:

[![enter image description here](https://i.sstatic.net/CJ6TK.png)](https://i.sstatic.net/CJ6TK.png)

The large steady dip is the main body of the asteroid passing over the V magnitude 8.0 star HIP 41337 = SAO 60804 = BD= +37° 1857 = HD 70920, spectral type K0. The small dip is the satellite passing over the star.

**Note:**
It's strange to me that the discovery of binary asteroid systems is met with skepticism since the method is essentially the same method often used to detect extra-solar planets (the transit method explained nicely in this [answer](https://astronomy.stackexchange.com/questions/8605/if-alpha-centauri-as-solar-system-exactly-mirrored-our-own-what-would-we-be-ab/8628?r=SearchResults&s=6%7C0.0000#8628)).

> **Comments:**
> **username_0**: Wow, what an amazing story! Slightly related: [Who first reported the Crab pulsar's pulsing but was dismissed by an astronomer?](https://hsm.stackexchange.com/q/11298/3869) Hmm, *Loma Prieta* sounds familliar, I was in an earthquake of the same name. In 1980 I think amateur astronomers timing occultations in the field had to either use visual timing or invest in and battery-power a photomultiplier tube and a tape recorder in order to record time resolved photometry, IAU should not have rejected the observation.  
> **username_5**: @username_0 There sure are a lot of cases in math and science where a discovery actually happened much earlier than the attributed date by someone other than the attributed discoverer.  I would be quite curious what the timing method and video method was used in 1980.  The 2012 Agamemnon occultation observations employed these systems: http://scottysmightymini.com/ .  I bet some similar systems were used for Arrokoth.  
> **username_0**: Yes indeed. That's a great question and I have a hunch that its asking will be forthcoming...  

---

