Astronomers may have found the first exomoon

https://www.eso.org/public/news/eso2610/

49•MarcoDewey•48m ago

Comments

bellowsgulch•41m ago

I nominate Moon 2: Electric Boogaloo.

pelagicAustral•39m ago

I know this is besides the article and all, but why would the Chilean flag be the only one to have 8px left margin? This is killing me...

    <div style="margin-left: 8px" title="Chile" class="sprites-flag_cl"></div>

inventor7777•37m ago

Now I can't unsee it :/

molf•34m ago

I believe such organisations tend to do such things very intentionally :-)

About ESO [1]

> We are an intergovernmental organisation established in 1962 supported by 16 Member States (Austria, Belgium, Czechia, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), our host country Chile and strategic partners.

So Chile has a distinct status, hence the margin...?

[1]: https://www.eso.org/public/about-eso/

pelagicAustral•25m ago

Granted, makes sense...

benabbott•37m ago

this would actually be a planet, based on my understanding of celestial bodies? moons are natural satellites orbiting planets. this "moon" is orbiting a brown dwarf.

eamag•32m ago

First paragraph:

> The star is being orbited by a brown dwarf, an object too massive to be a planet but too small to be a star.

catigula•20m ago

>According to the IAU working definition (from August 2018) an exoplanet can orbit a brown dwarf. It requires a mass below 13 MJ and a mass ratio of M/Mcentral<2/(25+√{621}), or roughly 1/25. This means that an object with a mass up to 3.2 MJ around a brown dwarf with a mass of 80 MJ is considered a planet. It also means that an object with a mass up to 0.52 MJ around a brown dwarf with a mass of 13 MJ is considered a planet

Foskya•31m ago

I guess it is more of a derivative of the question: "in which bucket should we put the brown dwarf? Is it a star or a planet?". The answer is neither of course; but since it is more closely related to stars than to planets, I'm more inclined to call this satellite an exoplanet (instead of exomoon).

That being said it is still a nice finding, way more difficult to discover than "normal" exopanets.

selectodude•27m ago

I thought we’re supposed to call them dwarf planets now. Dwarf star, dwarf planet.

HelloUsername•30m ago

An important phrase from the article to consider before commenting: "This system is somewhat hard to define using Solar-System-based words like ‘planet’ and ‘moon’"

hdz•28m ago

A small dense planet, which orbits a star, is orbited by a larger gaseous moon. It's interesting the discovery is in Chile which has some of the best night skies, a Class 1 on the Bortle scale specifically in the Atacama Desert. Hoping to make it out there one day.

walrus01•28m ago

> Instead, it circles a brown dwarf, an object larger than a planet, that orbits the CD-35 2722 star.

Isn't the dividing line between the largest possible gas giants and the smallest brown dwarfs a bit fuzzy?

https://en.wikipedia.org/wiki/Substellar_object

delta_p_delta_x•24m ago

The definition of a brown dwarf is that there is enough heat and compression for deuterium and/or lithium fusion, but not protium fusion.

The exact model limit is unclear, but the physics modelling is relatively straightforward.

bluGill•23m ago

I wonder if this thing in turn has something in orbit around it? At the size I wouldn't surprise me if it had satellites of its own in orbit, leaving open the question of what to call them. (I'm no astrophysicist, is this really possible I don't know, but it wouldn't surprise me. What would surprise me is if we could detect them)

jayGlow•15m ago

I had to look it up and it is theoretically possible, they could be called sub moons or moonmoon. I'm partial to the name moonmoon personally.

Someone•11m ago

https://en.wikipedia.org/wiki/Subsatellite:

“A subsatellite, also known as a submoon, moonlet or informally a moonmoon, is a "moon of a moon" or a hypothetical natural satellite that orbits the moon of a planet”

delta_p_delta_x•18m ago

Worth noting that the artist's impression is... not accurate. Both CD-35 2722 b (the brown dwarf orbiting the primary star) and CD-35 2722 b I (the exomoon orbiting the secondary) should be much closer in size. It is estimated that Jupiter is essentially the largest any gas giant can get; adding more mass will simply increase density and interior temperature until deuterium and lithium fusion and brown dwarfdom, and then at around 80 Jupiter masses, protium fusion and stardom.

Look at Barnard's Star[1], which is actually a fusing red dwarf star: it is not much bigger than Jupiter.

[1]: https://en.wikipedia.org/wiki/Barnard%27s_Star

PowerElectronix•16m ago

I really wanna call it a planet. It doesn't orbit a proper star, but if we call similar objects that don't orbit a star at all rogue planets I don't see why not call it just a planet.

_joel•12m ago

Brown dwarfs fascinate me, they can be at room temperature (range from about 2,800 K down to 250 K (roughly 2,500 °C to -23 °C / 4,500 °F to -10 °F)

You could basically have a bath in a brown dwarf, sure you might not last long, but still...

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