Astronomy

We are learning new things from Cassini's long visit at the moon, Titan, especially seasonal changes in it polar regions. See http://www.universetoday.com/131636/...amic-business/

It is good that missions last a while so we can observe such seasonal changes.

How many planets are there in our galaxy? A simple question but no simple answer. We have only recently realised just how many planets there are likely to be. See http://www.universetoday.com/30296/h...in-the-galaxy/. We don't even know how many stars there are in our galaxy (The Milky Way). So any attempt to enumerate the planets in the galaxy is even more difficult. Of these, only a tiny fraction can be habitable.

Cassini has been at Saturn now since 2004, and is about to plunge between the rings of Saturn and investigate them.

http://www.space.com/34488-cassini-f...w-science.html

http://www.universetoday.com/131677/...ly-downloaded/. This shows how long it takes to download information on the flyby of Pluto that New Horizons made. Well over a year in this case. New Horizons has continued deeper into the Kuiper Belt, making for a flyby of an object there that is mentioned in an earlier post on p.56.

The article shows there were constraints the New Horizon designers were up against, but it doesn't say exactly what they were. For some reason, the craft could only have a limited power output of 2-10 watts. It could only have a low downlink rate of 1-4 kilobits per second. And it had limited memory since they will have to erase its hard drive so it could continue collecting data for an extended mission.

I would think some of these constraints could be relaxed in future missions with better technology.

Neptune and Uranus: the two outer ice giants of the family of solar planets. Each is described and discussed for what little we know of them:

http://www.universetoday.com/21581/neptune/

http://www.universetoday.com/18855/uranus/

Just about the only information we have on Neptune the large gas giant (and the furthest out of all the planets except the dwarf planet Pluto) is the flyby that Voyager 2 did way back in 1989. See preceding post for the link on Neptune. Neptune has 14 known moons and also five rings around it. But a further visit to this distant and little-known planet might be worth making, perhaps in conjunction with a visit to Uranus. Uranus has 13 "inner moons" and nine "irregular moons". It also has 13 distinct rings around it. Again only Voyager 2 has done a flyby, though there are tentative plans for further visit. It rotates on it's side which is unique among the giant planets.

There is a graph in this link showing the axis of rotation of the various planets with some speculation on why we see such divergence: https://www.quora.com/Why-do-Venus-a...-anticlockwise

Although Uranus rotates on its side, Venus rotates upside down. That is, it rotates in the opposite direction to Earth's rotation.

Yes,its speculation, much like Velikovsky speculated that Venus was a captured comet, but as with all such ideas we don't really know why.

http://www.space.com/16144-kuiper-belt-objects.html.

This discusses the main kuiper belt objects we know a bit about today, including the mysterious Planet 9.

A link in that article led to one on the Oort cloud: http://www.space.com/16401-oort-clou...icy-shell.html

It helped me see the difference between the Kuiper belt and the Oort cloud.

http://www.space.com/34555-how-many-...able-zone.html

An interesting article on habitable planets.

It is interesting from the article that red dwarfs can last trillions of years and most of the stars are red dwarfs.

Not many people read the articles in the links. So I will just elaborate on the reasons why red dwarf stars are of interest in this context:

Van Laerhoven and her colleagues focused on K and M type stars, also known as red dwarfs. These stars are small, cold and about one-fifth the sun's mass and up to 50 times fainter. Red dwarfs constitute up to 70 percent of the stars in the universe, and NASA's Kepler spacecraft has discovered that at least half of these stars host rocky planets that are one-half to four times the mass of Earth.

Red dwarf planets are potentially key places to search for life, not just because there are so many of them, but also because of their incredible longevity. Unlike the sun, which will die in a few billion years, red dwarfs will take trillions of years to burn through their fuel, significantly longer than the age of the universe, which is about 13.8 billion years old. This longevity may give life ample time to develop on the planets that orbit these stars.

The habitable zones of red dwarfs fall close to these stars because of how cool they are — often closer than the distance at which Mercury orbits the sun. This closeness makes red dwarfs appealing to scientists hunting for habitable worlds, since planets in those habitable zones will cross in front of their star more often, making them easier to detect than planets that orbit farther away.

For the new research, the scientists carried out computer simulations involving a red dwarf about half the sun's mass, surrounded by a number of rocky planets with the same mass as Earth revolving around the star in circular orbits. These simulations each lasted up to 10 billion orbits of the innermost planet in each system. A planet at the inner edge of such a red dwarf's habitable zone would take only about one-fifth of an Earth-year to complete an orbit, Van Laerhoven said.