2026 ED138: A new candidate Dwarf Planet in the Kuiper Belt.

In the late twentieth century, our model of the Solar System was relatively simple, with nine planets orbiting the Sun, some of which had moons and rings, plus a variety of smaller comets and asteroids. The smallest of these planets, Pluto, was somewhat of an oddity, being smaller several of the Solar System's moons, including our own, and having a highly eccentric orbit which crossed the orbit of another planet, Neptune, but was clearly still to large a be a comet or asteroid. However, in the early twenty first century, this model began to change, with the discovery of a series of Pluto-like bodies beyond Neptune starting with Quaoar in 2002, then Sedna in 2003, Orcus and Haumea in 2004, and Eris and Makemake in 2005. This led the International Astronomical Union to reconsider how bodies within the Solar System are classified, coming up with a new category of objects, 'dwarf planets', in 2006. 

Dwarf planets are defined as objects large enough to have become rounded under the influence of their own gravity, but not large enough to have cleared their orbital path of other objects. Pluto was reclassified as a dwarf planet, losing its status as the Solar System's smallest planet, as was Ceres, the largest body in the Main Asteroid Belt, along with the newly discovered bodies Quaoar, Sedna, Orcus, Haumea, Eris, and Makemake. This list has subsequently grown with the addition of bodies such as Salacia and Gonggong.

In a press release issued on 27 October 2026, the Vera C. Ruben Observatory, which is located on Cerro Pachón in Chile, announced the discovery of a new candidate dwarf planet, 2026 ED138, which was discovered by astronomer Matthew Holman of Harvard University, who was analysing data collected by the Ruben Observatory, looking for moving objects in the outer Solar System.

Holman found 30 observations of the new object made by the Ruben Observatory between 4 March and 11 July 2026, which provided him with enough data to discover additional sightings in imagery from the Dark Energy Camera on the the Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory, and the Asteroid Institute’s ADAM Precovery service, with the oldest images dating back to 1937. 

A mosaic of images captured by NSF–DOE Vera C. Rubin Observatory of the newly discovered dwarf planet candidate 2026 ED138. 2026 ED138 was discovered in observational data from Rubin spanning 4 March–11 July 2026. It was found by Rubin Operations team member and in-Kind contributor Matthew Holman, who contributes to improving Rubin's algorithms that search for distant moving objects in our Solar System. Its distance from the Sun places it beyond the orbit of Pluto, and initial analysis indicates that it may be among the largest and brightest bodies scientists have discovered in this region of the Solar System. Vera C. Rubin Observatory/NOIRLab/SLAC National Accelerator Laboratory/AURA Image Processing/Mario Jurić/Davide de Martin/Mahdi Zamani.

The designation 2026 ED138 implies that it was the 2454th asteroid (object D138 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 25, with a number added to the end each time the alphabet is ended so that A = 1, A1 = 26, A2 = 51, etc., which means that D138 implies the (138 x 25 + 4) 2454th asteroid) discovered in the first half of March 2026 (period 2026 E - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

2026 ED138 is currently about 47.225 AU from the Sun (where 1 AU is the average distance between the Earth and the Sun), with an orbital period estimated at 281 years, which will bring it as close as 36.86 AU from the Sun and as far as 49.04 AU. As an object which has an orbit entirely outside the orbit of Neptune, it is a trans-Neptunian Object, and having a low-eccentricity (approximately circular) orbit, it is a Classical trans-Neptunian Object. This orbit is tilted at 24.5° to the plain of the Solar System, making 2026 ED138 a Hot Classical trans-Neptunian Object; a Classical trans-Neptunian Object with an orbit tilted at more than 5° to the plain of the Solar System. Such objects are thought to have been disturbed from the plain of the Solar System by gravitational interactions with the planet Neptune.

The relative positions of 2026 ED138, the Earth, and the planets of the Outer Solar System on Sunday 1 November 2026. JPL Small Body Database.

2026 ED138 is a bright object, with an absolute magnitude estimated to be between 2.85 and 3.19. This would make it the ninth or tenth brightest trans-Neptunian Object discovered to date. From this brightness it is estimated that it has a diameter of between 600 and 1500 km. This variation stems from an uncertainty as to whether it has a bright surface, which would place it at the lower end of this range, or a dull one, which would place it towards the upper end, and make it a Dwarf Planet. Potential observations of the object with infrared telescopes, observations of stellar occulations (events in which it passes in front of a star), and possibly direct observations with the James Webb Space Telescope could tell us more about its nature.

The orbital period of 2026 ED138 suggests that it is locked into a 12⁄7 orbital resonance with Neptune. This is roughly the same as that of the dwarf planet Haumea, as well as a group of objects called the Haumean Family of trans-Neptunian Objects. However, it is not currently thought to be a member of that family due to the difference in its albedo (brightness) to that of Haumea and the Haumean Family objects.

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Dwarf Planet 136199 Eris approaches opposition.

The dwarf planet 136199 Eris will reach opposition (i.e. be directly opposite the Sun seen from Earth) on Sunday 18 October 2026 at 6.32 pm GMT. This means that it will both be at its closest to the Earth this year, about 94.47 AU (94.47 times the average distance between the Earth and the Sun, or about 14, 133 000 000 km), and completely illuminated by the Sun. While it is not visible to the naked eye observer, the planets have phases just like those of the Moon; being further from the Sun than the Earth, 136199 Eris is 'full' when directly opposite the Sun. 

The orbit and position of 136199 Eris and selected Solar System planets at 7.00 pm GMT on Sunday 18 October 2026. JPL Small Body Database Browser.

Although this coincides with a First Quarter Moon, the prospects for viewing without a very powerful telescope are not as good. The dwarf planet will be in the constellation of Cetus and will be at its highest point in the sky at about midnight local time, from anywhere on Earth (this is because the rising and setting of objects in the sky is caused by the Earth's rotation, not the movement of the object). (Even at it's very brightest 136199 Eris will only have a Magnitude of 18.6, making it almost impossible to see with any but the largest of Earth-based telescopes, and where resolvable it will only be possible to see it as a point of light indistinguishable from a faint star.

136199 Eris orbits the Sun on an eccentric orbit tilted at an angle of 44.1° to the plane of the Solar System, which takes it from 35.9 AU from the Sun (35.9 times the average distance at which the Earth orbits the Sun) to 97.5 AU from the Sun (97.5 times the average distance at which the Earth orbits the Sun. With an average distance of 67.74 AU, 136199 Eris completes one orbit around the Sun every 558 years. This means that the planet is almost stationary compared to the faster moving Earth, so that it reaches Opposition only four days later each year than the year before, and reaches Solar Conjunction (when it is directly on the opposite side of the Sun to the Earth), roughly six months later.

136199 Eris was discovered on 5 January 2005 by a team led by Mike Brown of the Palomar Observatory in California. With a diameter of 2326 km it is considered to be the second largest dwarf planet in the Solar System (after 134340 Pluto) as well as the sixteenth largest body in the Solar System, excluding the Sun (though several moons, including our own, are larger). It is also the largest body in the Solar System never to have been visited by a spacecraft (again, with the exception of the Sun). 136199 Eris has a single moon, Dysnomia, which has a diameter of about 700 km and obits at a distance of about 37 350 km.

Labelled Hubble Space Telescope Image of 136199 Eris, showing its satellite Dysnomia. Captured on 12 June 2007. Mike Brown/NASA/European Space Agency/Wikimedia Commons.

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The Alpha Aurigid Meteor Shower.

The Alpha Aurigid Meteor shower occurs each year between 25 August and 6 September, and is expected to peak between 1.00 am and dawn on 1 September (this should be roughly the same wherever you are, as our 24 hour clock is derived from the motion of the Earth). However the shower is notoriously hard to observe, having been recorded only in the years 1911, 1929, 1930, 1935, 1979, 1980, 1986, 1994 and 2007 (some of these observations occurred before the 'official' discovery of the shower by Cuno Hoffmeister and Artur Teichgraeber in 1935, but have subsequently been linked to the shower). To make matters worse, the peak of the shower will fall slightly after the New Moon on 28 August, which would hamper the viewing of any meteors that do appear. The shower has its radiant point (the point from which the meteors appear to radiate) in the constellation of Auriga, close to the star Alpha Auriga (hence the name), which is a circumpolar star, permanently above the horizon in the Northern Hemisphere, but difficult to spot from the Southern Hemisphere.

The radiant of the Alpha Aurigid Meteors. Copper Mountain Mesa.

Meteor showers are thought to be largely composed of material from the tails of comets. Comets are composed largely of ice (mostly water and carbon dioxide), and when they fall into the inner Solar System the outer layers of this boil away, forming a visible tail (which always points away from the Sun, not in the direction the comet is coming from, as our Earth-bound experience would lead us to expect). Particles of rock and dust from within the comet are freed by this melting (strictly sublimation, transforming directly from a solid to a gas due to the low pressure on it's surface) of the comet into the tail and continue to orbit in the same path as the comet, falling behind over time.

The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob. 

The Aurigid Meteors are made by the Earth passing through the trail of Comet C/1911 N1 (Keiss),  and encountering dust from the tail of this comet. The dust particles strike the atmosphere at speeds of over 200 000 km per hour, burning up in the upper atmosphere and producing a light show in the process.

How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

Comet C/1911 N1 (Keiss) was discovered on 6 July 1911, by astronomet Carl Clarence Keiss, at the Lick Observatory on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California. The name C/1911 N1 (Keiss) implies it was the first (1) comet (C/) discovered in the first half of July 1911 (period 1911 N), and that is was discovered by Keiss.

A photograph of Comet C/1911 N1 (Keiss) taken by French Astronomer Ferdinand Quénisset at the Camille Flammarion Observatory to the south of Paris on 29 July 1911. The photograph is a single 78 minute exposure which tracked the comet; the elongated objects are stars which moved during the course of the exposure. Wikimedia Commons.

Comet C/1911 N1 (Keiss) completes one orbit every 2497 years on an eccentric orbit tilted at 148° to the plane of the Solar System, that takes it from 0.68 AU from the Sun (68% of the average distance at which the Earth orbits the Sun, and slightly inside the orbit of the planet Venus) to 367 AU from the Sun (367 times as far from the Sun as the Earth, and more than three times the distance at which the planet Neptune orbits the Sun). The comet last visited the Inner Solar System in 1911. As a comet with an orbital period of more than 200 years it is considered to be a Long Period Comet.

The current position and orbit of C/1911 N1 (Keiss). JPL Small Body Database.

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Partial Lunar Eclipse to be visible from West Africa and much of the Americas.

A partial Lunar Eclipse will occur on Friday 28 August 2026, starting at 1.25 am GMT. The whole eclipse will be visible across all of South America and the Atlantic, and most of North America, and most of West Africa and the western Maghreb, and western Iberia while part of the eclipse will be visible from parts of the northwest of North America, the remaining parts of the Maghreb and West Africa, as well as much of Central and Southern Africa, European Russia, the remainder of the Middle East, and Western and Central Europe, and parts of Norway. although in these areas the Moon will either rise part way through the eclipse, or set before it is complete.

Areas from which the 28 August 2026 Lunar Eclipse will be visible. Dominic Ford/In the Sky.

The Moon produces no light of its own, but 'shines' with reflected light from the Sun. Thus, at Full Moon the Moon is on the opposite side of the Earth to the Sun, and its illuminated side is turned towards us, but at New Moon the Moon is between the Earth and the Sun, so that its illuminated side is turned away from us.

Lunar eclipses occur when the Moon passes through the Earth's shadow. This can only happen at Full Moon (unlike Solar Eclipses, which happen only when the Moon passes between the Earth and the Sum, and therefore only occur at New Moon), but does not happen every Lunar Month as the Sun, Moon and Earth are not in a perfect, unwavering line, but rather both the Earth and the Moon wobble slightly as they orbit their parent bodies, rising above and sinking bellow the plane of the ecliptic (the plane upon which they would all be in line every month).

How the differing inclinations of the Earth and Moon's orbits prevent us having an eclipse every 28 days. Starry Skies.

Because the Moon is passing through a shadow, rather than being blocked from our view, it does not completely disappear during an eclipse like the Sun, but in a total Lunar Eclipse goes through two distinct phases of dimming, the Penumbra, when it is still partially illuminated by the Sun, and the Umbra, when the Earth completely blocks direct sunlight from the Moon. This does not result in complete darkness, as the Moon is still partially lit by reflected Earthlight, but it does turn a deep, dark red colour.  In a partial eclipse the Earth passes completely through the Moon's penumbra, but only partly through its umbra.  

The phases of the 3 March 2026 Lunar Eclipse. Leah Tiscione/Sky & Telescope.

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The Kappa Cygnid Meteor Shower.

The Kappa Cygnid Meteor Shower is visible some years between the months of June and September, peaking between 3 and 25 August, with the best peak rate generally falling before dawn on 18 August, when the shower can produce 2-3 meteors per hour, with these tending to be bright fireballs with multiple fares. The meteor shower gains its name from the star Kappa Cygnus, which it is close to at the peak of its activity, and which is circumpolar in the Northern Hemisphere (i.e., close to the North Pole, and permanently above the horizon), although generally invisible in the Southern Hemisphere. If the shower does appear, viewing should be reasonably good, as activity will peak two days before the first quarter Moon, which will be in the constellation of Virgo, providing minimal light interference. However, the meteor shower is notoriously erratic, not being seen every year; it was last seen in the Augusts of 2020 and 2021, and before that in 2013 and 2014, then before that in 2007.

The radiant point of the Kappa Cygnid Meteor Shower. The Sky Live.

Meteor showers are thought to be largely composed of material from the tails of comets. Comets are composed largely of ice (mostly water and carbon dioxide), and when they fall into the inner Solar System the outer layers of this boil away, forming a visible tail (which always points away from the Sun, not in the direction the comet is coming from, as our Earth-bound experience would lead us to expect). Particles of rock and dust from within the comet are freed by this melting (strictly sublimation, transforming directly from a solid to a gas due to the low pressure on it's surface) of the comet into the tail and continue to orbit in the same path as the comet, falling behind over time.

The Earth passing through a stream of comet dust, resulting in a meteor shower. Not to scale. Astro Bob.

The source body of the Kappa Cygnid Meteors remains somewhat of an enigma. The low number of asteroids, and their irregular arrival, suggests they are an old shower potentially derived from an object no longer visiting the Inner Solar System, whereas the brightness of the meteors suggests a younger origin. One possible solution to this is that they are derived from a body whose orbit undergoes a sinusoidal oscillation, something which can be caused if a body is forced into an orbital resonance with a larger body, often Jupiter in our Solar System. 

How the passage of the Earth through a meteor shower creates a radiant point from which they can be observed. In The Sky.

One potential parent body for the Kappa Cygnid Meteors which has been suggested is 2008 ED69, an asteroid which has an orbit with a 2:1 resonance with that of Jupiter and an orbital period of 4.96 years, which is thought to have been pushed into and out of Earth-crossing orbits repeatedly over the past 6000 years. However, more recent studies have established that the Kappa Cygnid Meteor Shower has an orbital period of 7.12 years and is locked into a 5:3 orbital resonance with Jupiter, ruling out 2008 ED69 as a potential parent body.

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