what if the sun were half as big?

A smaller star might last longer, but Earth would be a very dif­fer­ent planet

How It Works - - SCIENCE -

Earth sits in an or­bit around the Sun called the hab­it­able zone. This ‘Goldilocks’ re­gion of stel­lar space is not too hot and not too cold, just right for liq­uid water to flow freely in Earth’s lakes, rivers and oceans. The po­si­tion of this zone de­pends on the size of our star, and if the Sun sud­denly halved in mass ev­ery­thing would change. The Sun is a G-dwarf star, also known as a yel­low dwarf. It fuses hy­dro­gen atoms to­gether to make he­lium, gen­er­at­ing a sur­face tem­per­a­ture of be­tween 5,300 and 6,000 Kelvin (around 5,000 to 5,700 de­grees Cel­sius). A star half its size would be an M-dwarf star, also known as a red dwarf, with a much lower tem­per­a­ture of be­tween 2,500 and 4,000 Kelvin (2,200 to 3,700 de­grees Cel­sius). To keep our water liq­uid around this kind of star we’d need to or­bit much closer, and that would cause some prob­lems. Hud­dling close to a red dwarf star would gen­er­ate strong tidal forces. This would slow Earth’s spin, length­en­ing our days. It’s pos­si­ble that we’d de­cel­er­ate so much that we’d be­come locked in one ori­en­ta­tion, with one side of the planet al­ways in day­light and the other in per­pet­ual dark­ness. If this hap­pened our water might freeze or boil away, leav­ing Earth bar­ren and life­less.

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