Tuesday, March 22, 2016

Some Water and an HMI Roll Please!

Today is World Water Day, when we think about how important water is to our lives. Without clean water we cannot survive, so take a minute to remember all the people who bring clean, fresh water to your house.

But water also plays an important role in the far future of the Earth. Right now the average temperature of the Earth is a comfortable 60°F. This is a balance between the heat coming from the Sun and the heat lost by the Earth. That temperature would be about 280 K (45°F) without our atmosphere. It would also be very hot in the day and very cold at night. The Earth's average surface temperature is higher (and varies less) because we have an atmosphere that retains some of the heat. Water and carbon dioxide are the main gases that warm the planet's surface.

That delicate balance will be affected by the increase in the solar irradiance over the next billion years. At that time the average temperature of the Moon will exceed the boiling point of water. The effect on the Earth could be quite dramatic. The oceans will evaporate and we will have a steam atmosphere whose surface temperature will cause rocks on the surface to break down. The actual calculations depend on the details of the solar input and how steam (or water) stops heat from leaving the atmosphere.

And water plays a role in the ultimate fate of our planet. When the Sun exhausts the hydrogen fuel being used to create heat in the core, it enters new stages of evolution. One of these is to become a red giant star, whose size can reach 1 AU (the Earth's orbit) or larger. Rather than a small dot in the sky the Sun would be huge red disk! A red giant is very cool (compared to today's Sun) and molecules such as water can form in the atmosphere. The actual size depends on how that water interacts with the light becoming from inside the Sun. Changing how water interacts can shrink the red giant so that it encompasses Venus or enlarge it to encompass Mars.

So, on World Water Day, it is good to think how important water is, both to our lives today and the Earth tomorrow.

On an operational note: We will roll SDO 180° tomorrow for 25 hours starting at 1900 UTC (3:00 pm ET). This is designed to help the HMI team understand how their data is behaving. Some SDO near-realtime data may be upside down for awhile as the data system adapts to the new attitude.