Moon and ExoMoons.

Exposure: best 25% of 500 video frames

Image date: 2021-06-17

The dark regions are Mare Nectaris (top centre); and Mare Tranquilitatis (top left) where the Apollo 11 landing site Tranquility Base is still located. The large crater at the intersection of the two Mares is about 100km in diameter and 4.2 km in depth and it’s called Theophilus Crater.

Where is Tranquility Base?

Astronomers theorise that the Moon was formed about 4.5 billion years ago from debris created from a collision between Earth and an object the size of Mars, not long after the Solar System itself had formed.

Why am I telling you this? It’s just an excuse to lead into my Astronomy News of The Week:

Astronomy News of the Week

Astronomers spot a protoplanetary disc

Radio astronomers have, incredibly, made the first ever discovery of a circumplanetary disc around an exoplanet in another star system, contributing to the growth of the exoplanet and crating an environment where moons are likely to form.

The ALMA radio image below shows a large circumstellar disc with the host star PDS 70 at the centre. It reminds you of Saturn, you may say. Well, it’s a helluva lot bigger than Saturn.

The PDS 70 system is 400 light years away and solar system sized!

Inside the circumstellar disc is an exoplanet PDS 70c, a T-Tauri class star (young and variable in magnitude) with its own circumplanetary disc, which astronomers theorise could eventually form into one or more natural exosatellites. Moons!

It’s one thing to image a circumstellar disc, (many are known). It’s another thing entirely to spot a circumplanetary disc!

Click the image to see the ESO data page in a new tab:

This image, taken with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, shows the PDS 70 system, located nearly 400 light-years away and still in the process of being formed. The system features a star at its centre and at least two planets orbiting it, PDS 70b (not visible in the image) and PDS 70c, surrounded by a circumplanetary disc (the dot to the right of the star). The planets have carved a cavity in the circumstellar disc (the ring-like structure that dominates the image) as they gobbled up material from the disc itself, growing in size. It was during this process that PDS 70c acquired its own circumplanetary disc, which contributes to the growth of the planet and where moons can form.

The strange thing is that astronomers used to believe that the Moon formed from a circumplanetary disc during the formation of the solar system. They have since come to believe this unlikely and that the collision theory I mentioned above was the likely cause.

Yet in contrast, here we have a prime example, our very first view of a circumplanetary disc in a nearby stellar system which is possibly forming moons right now!

This exquisite radio image is one of the reasons why astronomy is so exciting!

Thanks for reading 🙃

Telescope & Imaging Details (Lunar Image)

Telescope:	SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Optics:	Field flattener; no filter.
Mount & Guiding:	SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.
Imaging camera:	ZWO ASI 290 MC uncooled.
Software:	Control: Cartes du Ciel, ASCOM, EQMOD, PHD2. Imaging: SharpCap, Gimp.
Observatory:	34° South.

Lunar image © Roger Powell
I’m one of the founder members of Macarthur Astronomical Society and current webmaster.

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