{"id":53433,"date":"2024-01-12T06:02:12","date_gmt":"2024-01-12T06:02:12","guid":{"rendered":"http:\/\/16016c3a-e328-4459-9917-8953b8db16e6"},"modified":"2024-01-12T08:33:49","modified_gmt":"2024-01-12T08:33:49","slug":"whats-the-smallest-planet","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/whats-the-smallest-planet\/","title":{"rendered":"What’s the smallest planet?"},"content":{"rendered":"

What’s the smallest planet in our Solar System, and what’s the smallest known exoplanet? <\/p>

By Russell Deeks\n <\/p>

Published: Friday, 12 January 2024 at 06:02 AM<\/p>

\n\n

If you\u2019re talking about planets in our Solar System, that\u2019s easy to answer: the smallest planet is Mercury.<\/p>

Mercury is the smallest of all the eight planets whether you\u2019re looking at ‘size’ in terms of radius, volume or mass.<\/p>

By radius and volume, Mercury<\/a> is the 11th<\/sup> largest object in the Solar System, after the Sun, the other seven planets, Jupiter\u2019s moon Ganymede and Saturn\u2019s moon Titan.<\/p>

If you’re talking mass then Mercury, being denser, leapfrogs Titan and Ganymede to be the 9th most massive object in the Solar System.<\/p>

Quick answers: Why are planets round<\/a>? How many planets are there<\/a>? What are the colours of the Solar System planets<\/a>?<\/em><\/strong><\/p>

View of Mercury captured by the MESSENGER spacecraft. Credit: Source: NASA\/Johns Hopkins University Applied Physics Laboratory\/Carnegie<\/figcaption><\/figure>

Mercury’s size by numbers<\/strong><\/h2>

To put some actual numbers on that, Mercury has a radius of around 2,440km, just over a third the radius of Earth.<\/p>

It has a volume of 6.083 x 1010 <\/sup>km3<\/sup>, or just over 1\/18th<\/sup> of Earth\u2019s volume, while its mass of 3.3011 x 1023<\/sup> kg is just a smidgeon less than 1\/18th<\/sup> that of Earth.<\/p>

By way of comparison, Jupiter \u2013 the largest Solar System planet \u2013 has a radius of 69,911km, nearly 11 times that of Earth.<\/p>

\"Mercury
Mercury is the smallest planet in the Solar System. Its silhouette in front of the Sun shows how it is absolutely dwarfed by our host star. Credit: ESA\/NASA Solar Orbiter<\/figcaption><\/figure>

Jupiter’s volume is 1,321 times greater than Earth\u2019s and its mass is just under 318 times that of Earth.<\/p>

That makes Jupiter over 23,500 times larger than Mercury by volume.<\/p>

Of course, it hasn\u2019t always been this way\u2026 until 1996, the smallest planet was Pluto.<\/p>

But following the discovery of Eris and other large trans-Neptunian objects, Pluto was downgraded to ‘dwarf planet’ status, leaving Mercury as the Solar System\u2019s smallest planet proper.<\/p>

Smallest exoplanet<\/strong><\/h2>
\"Artist's
Artist’s impression of exoplanet Kepler 37b, one of the smallest known planets. Credit: NASA<\/figcaption><\/figure>

As for exoplanets<\/a> \u2013 those outside our own Solar System \u2013 it\u2019s much harder to say which is the smallest planet.<\/p>

With current technology, we can only really detect the largest exoplanets.<\/p>

While it\u2019s possible to say the smallest exoplanet discovered so far is Kepler-37b, considerably smaller than Mercury and only a little bigger than our own Moon, we can\u2019t know for sure that there aren\u2019t billions of tiny planets out there that would make poor little Mercury look positively Jovian!<\/p> <\/body><\/html>\n

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