<p>The confusion comes from the difference between the nucleus and the coma.</p>

<p>The nucleus is a small icy body, only a few km across.</p>

<p>The coma is the cloud of gas and dust released from the nucleus as it warms up.  With not much gravity, the coma spreads out into space, and it can be hard to say exactly where the edge of the coma lies, however, a coma "the size of Jupiter" would not be unusual. Active comets can have comas that are larger than the sun.</p>

<p>But the mass of the coma is tiny. It is made of a very low-pressure gas. It is nearly all empty space, most of the mass of the comet remains locked in the nucleus.</p>

CC BY-SA 4.0
2020-04-04T07:52:03.457Z
2020-04-04T07:52:03.457Z
James K
<p>I read some news about this new comet and some unreliable sources said it is twice as big as Jupiter. I tried to find a reliable estimation of its size or mass, but I couldn't find anything. Would you please provide me a general way to distinguish reliable facts from unreliable facts about comets? Like their size and mass range, how much mass they lose, etc.</p>

CC BY-SA 4.0
2020-04-04T10:24:38.997Z
I don't know about this comet at the moment, but a [comet's coma](https://en.wikipedia.org/wiki/Coma_(cometary)) could certainly appear twice as large as Jupiter in a pair of binoculars or a telescope especially if the comet was closer to Earth than Jupiter (which they are when they become visible). The coma is just a cloud-like thing that reflects some sunlight, the actual comet is very tiny and by itself would be extremely hard to see and certainly not have a discernible size.
uhoh
<jupiter><comets><mass><size>
Size and mass of comet ATLAS (C/2019 Y4)
abbassix
# Size and mass of comet ATLAS (C/2019 Y4)

(Asked by: username_0 on 2020-04-04)

I read some news about this new comet and some unreliable sources said it is twice as big as Jupiter. I tried to find a reliable estimation of its size or mass, but I couldn't find anything. Would you please provide me a general way to distinguish reliable facts from unreliable facts about comets? Like their size and mass range, how much mass they lose, etc.

**Tags:** jupiter, comets, mass, size
> **Comments:**
> **username_1**: I don't know about this comet at the moment, but a [comet's coma](https://en.wikipedia.org/wiki/Coma_(cometary)) could certainly appear twice as large as Jupiter in a pair of binoculars or a telescope especially if the comet was closer to Earth than Jupiter (which they are when they become visible). The coma is just a cloud-like thing that reflects some sunlight, the actual comet is very tiny and by itself would be extremely hard to see and certainly not have a discernible size.  

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## 1 answers

### Answer by username_2 on 2020-04-04. Score: 14 | Accepted answer

The confusion comes from the difference between the nucleus and the coma.

The nucleus is a small icy body, only a few km across.

The coma is the cloud of gas and dust released from the nucleus as it warms up. With not much gravity, the coma spreads out into space, and it can be hard to say exactly where the edge of the coma lies, however, a coma "the size of Jupiter" would not be unusual. Active comets can have comas that are larger than the sun.

But the mass of the coma is tiny. It is made of a very low-pressure gas. It is nearly all empty space, most of the mass of the comet remains locked in the nucleus.


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