Being in this ‘Goldilocks’ zone has allowed oceans to develop in temperatures neither too hot to boil the water away, or too cold to freeze
it into permanent ice.
The problem is, however, that stars become hotter over time, ensuring that the habitable period cannot last.
As the stars emit more heat, any surface water on nearby planets dries up and without water nothing can survive.
I was just reading the article and I don't understand how they end up with their prediction.
The Star Arcturus shines about 15 times brighter then the Sun, and it's mass is about 130 times that of the Sun. The temperature however is lower
then the temperature of the Sun.
Modern understanding of Arcturus
Today, astronomers know Arcturus packs a lot of punch despite it being only about 1.5 times the mass of the sun. To the naked eye, according to Jim
Kaler, a professor emeritus at the University of Illinois. Arcturus appears to shine about 113 times more brightly than the sun.
Arcturus, however, has a lower temperature than the sun, which means that a lot of its energy is radiated as heat. Once this is accounted for,
Arcturus actually releases 215 times more than the sun's radiation.
How do they predict the increase in temperature ?
Arcturus is said to be near the end of its lifespan, but is colder then the Sun. The fusion of heavier elements could explain why more heat gets
radiated, but what makes it shine so bright then ?
The Sun isn't nearly as bright, and it's still fusing hydrogen atoms, what could explain the higher temperature of the Sun.
However, if fusing higher elements causes less heat and more light, radiating out, like Arcturus shows.
How can it radiate more heat and shine more brightly, when the star itself is colder ?
Arcturus is also slightly larger then the Sun is, so I would expect it to runs out of hydrogen faster then the Sun would.
How can they predict anything about the Sun's temperature, when we are only able to observe and measure any data for only a brief moment of the
entire lifespan of our Sun, and any other Star for that matter ?
The Earth is protected by a magnetic field, which prevents our atmosphere getting blown of the planet, by solar wind etc.
So even if the Sun radiates more heat, and water starts to vaporize, it won't simply vanish. When night falls and temperatures plummet way below
freezing, everything without an atmosphere gets cold.
The atmosphere is what creates a stable environment. When the Sun gets hotter, the Earth will hold more heat, but if our atmosphere is filled with
water vapor, most of the heat won't even reach the surface, as the cloud cover would reflect it back into space. Everything below won't be receiving
much heat, and at night the atmosphere gets to cool down.
The Sun will also lose a lot of mass during its lifetime, as it gets blown into space. That could result in larger orbits of the planets, as gravity
is a little less.
Anyway... I just don't get it. An explanation is more the welcome.
What's the point of making these predictions, when it's pretty obvious, our knowledge about it is limited.