<p>The discovery announcement by the <a href="https://minorplanetcenter.net/mpec/K21/K21CI7.html" rel="nofollow noreferrer">Minor Planet Center</a> indicates that 2018 AG 37 (&quot;Farfarout&quot;) was between 25.0 and 25.3 magnitude. The positions are based on observations taken with the 8 m Subaru telescope and 6.5 m Magellan-Baade telescope.</p>
<p>As a comparison, this ancient article by Sky &amp; Telescope (<a href="https://skyandtelescope.org/astronomy-resources/astronomy-questions-answers/what-is-the-faintest-object-imaged-by-ground-based-telescopes/" rel="nofollow noreferrer">What Is The Faintest Object Imaged By Ground-Based Telescopes?</a>) indicates the Subaru telescope limit is around 27.7. (&quot;Ancient&quot; in terms of CCD cameras and computer processing. The article is from 2006.) Note that this same article indicates that a 16 inch (400 mm) amateur telescope should be able to capture images to 24th magnitude -- just 2x to 3x brighter than Farfarout!</p>
<p>Also, the <a href="https://hscq.naoj.hawaii.edu/cgi-bin/HSC_ETC/hsc_etc.cgi" rel="nofollow noreferrer">Subaru Exposure Calculator</a> indicates an exposure of 1 minute will capture a 25.3 magnitude object using default input (except for the Moon, which I set to New Moon).
<a href="https://i.sstatic.net/X7wKG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/X7wKG.png" alt="Exposure on Subaru telescope for 25.3 mag object" /></a></p>
<p>Thus, it seems almost &quot;easy&quot; to capture an image of it.</p>
<p>Finding an unknown, faint object is another issue. I do not have any information on this aspect of the question, but I feel safe that computer searches are quite adept at finding such things. Once the first image (or pair of images that show motion) is found, other images are often found or taken to facility the calculation of the orbit. The time span of the images is only two (2) years which is short for a body with a period of 1000 years (estimate). The Wikipedia page for <a href="https://en.wikipedia.org/wiki/2018_AG37" rel="nofollow noreferrer">2018 AG37</a> currently lists large uncertainties for the average distance (86 +/-68 AU) and period (798 +/-941 years). Those uncertainties will be reduced as a longer arc of the orbit is measured.</p>

CC BY-SA 4.0
2021-02-11T18:30:42.460Z
ok. so maybe finding it was not such a big deal as I initially thought.
Natsfan
CC BY-SA 4.0
2021-02-11T05:04:16.527Z
2021-02-11T05:04:16.527Z
JohnHoltz
<p>It was recently announced that the most distant object in our solar system was discovered. This object averages 132 AU from the sun. The <a href="https://en.wikipedia.org/wiki/2018_AG37" rel="nofollow noreferrer">object, initially named Farfarout</a>, was estimated to be 400 km across. How was such a small object found and its orbit estimated by a ground-based telescope? This seems to really be pushing the limits of observable objects. Or am I wrong on this?</p>
<p>Ref: <a href="https://phys.org/news/2021-02-astronomers-orbit-distant-solar.html" rel="nofollow noreferrer">https://phys.org/news/2021-02-astronomers-orbit-distant-solar.html</a></p>

CC BY-SA 4.0
2021-02-11T09:49:03.290Z
Note that other objects 'average', i.e. have a semi-major axis distance that is even farther out than Farfarout, such as 90377 Sedna. Such faint objects are challenging for any single observation, but digitalized before/after comparisons do a good job at finding these.
AtmosphericPrisonEscape
CC BY-SA 4.0
2021-02-11T18:34:22.213Z
@AtmosphericPrisonEscape,  thanks for you comment.
Natsfan
<observational-astronomy><planet><solar-system>
Recently, the most distant object in the solar system was discovered. How was this accomplished?
Natsfan
# Recently, the most distant object in the solar system was discovered. How was this accomplished?

(Asked by: username_0 on 2021-02-11)

It was recently announced that the most distant object in our solar system was discovered. This object averages 132 AU from the sun. The [object, initially named Farfarout](https://en.wikipedia.org/wiki/2018_AG37), was estimated to be 400 km across. How was such a small object found and its orbit estimated by a ground-based telescope? This seems to really be pushing the limits of observable objects. Or am I wrong on this?

Ref: <https://phys.org/news/2021-02-astronomers-orbit-distant-solar.html>

**Tags:** observational-astronomy, planet, solar-system
> **Comments:**
> **username_1**: Note that other objects 'average', i.e. have a semi-major axis distance that is even farther out than Farfarout, such as 90377 Sedna. Such faint objects are challenging for any single observation, but digitalized before/after comparisons do a good job at finding these.  
> **username_0**: @AtmosphericPrisonEscape,  thanks for you comment.  

---

## 1 answers

### Answer by username_2 on 2021-02-11. Score: 3 | Accepted answer

The discovery announcement by the [Minor Planet Center](https://minorplanetcenter.net/mpec/K21/K21CI7.html) indicates that 2018 AG 37 ("Farfarout") was between 25.0 and 25.3 magnitude. The positions are based on observations taken with the 8 m Subaru telescope and 6.5 m Magellan-Baade telescope.

As a comparison, this ancient article by Sky & Telescope ([What Is The Faintest Object Imaged By Ground-Based Telescopes?](https://skyandtelescope.org/astronomy-resources/astronomy-questions-answers/what-is-the-faintest-object-imaged-by-ground-based-telescopes/)) indicates the Subaru telescope limit is around 27.7. ("Ancient" in terms of CCD cameras and computer processing. The article is from 2006.) Note that this same article indicates that a 16 inch (400 mm) amateur telescope should be able to capture images to 24th magnitude -- just 2x to 3x brighter than Farfarout!

Also, the [Subaru Exposure Calculator](https://hscq.naoj.hawaii.edu/cgi-bin/HSC_ETC/hsc_etc.cgi) indicates an exposure of 1 minute will capture a 25.3 magnitude object using default input (except for the Moon, which I set to New Moon).
[![Exposure on Subaru telescope for 25.3 mag object](https://i.sstatic.net/X7wKG.png)](https://i.sstatic.net/X7wKG.png)

Thus, it seems almost "easy" to capture an image of it.

Finding an unknown, faint object is another issue. I do not have any information on this aspect of the question, but I feel safe that computer searches are quite adept at finding such things. Once the first image (or pair of images that show motion) is found, other images are often found or taken to facility the calculation of the orbit. The time span of the images is only two (2) years which is short for a body with a period of 1000 years (estimate). The Wikipedia page for [2018 AG37](https://en.wikipedia.org/wiki/2018_AG37) currently lists large uncertainties for the average distance (86 +/-68 AU) and period (798 +/-941 years). Those uncertainties will be reduced as a longer arc of the orbit is measured.

> **Comments:**
> **username_0**: ok. so maybe finding it was not such a big deal as I initially thought.  

---

