MESSENGER
Posted: Wed Mar 09, 2011 12:56 am
Just a heads up...MESSENGER is to enter orbit around Mercury on the 18th, just 10 days from now. It's been a long trip...
About the same amount of time it took Cassini to reach far more distant Saturn. Celestial mechanics, fascinating.Mjolnir wrote:Just a heads up...MESSENGER is to enter orbit around Mercury on the 18th, just 10 days from now. It's been a long trip...
And New Horizons zipped past Saturn orbit on its way to Pluto in just a couple years, ending its last burn with 16.26 km/s relative to Earth...in a different direction, that could put it in an elliptical orbit between 0.1 AU and 1 AU. Split across two burns in a direct Hohmann transfer, it would have fallen just short of Mercury's orbit around the sun, but gotten there in a couple months. To get to the sun itself (always quite close to 1 AU away), it would have to take an indirect approach...looping out to Jupiter and using its gravity well to change direction, perhaps. Or cheating and using a solar sail.Trantor wrote:About the same amount of time it took Cassini to reach far more distant Saturn. Celestial mechanics, fascinating.Mjolnir wrote:Just a heads up...MESSENGER is to enter orbit around Mercury on the 18th, just 10 days from now. It's been a long trip...
Mjolnir wrote: And New Horizons zipped past Saturn orbit on its way to Pluto in just a couple years
Not sure if you meant to imply that Mercury was tidally locked....it's actually in a 3:2 spin-orbit resonance. There's lots of permanently shadowed areas at the poles, though, and apparently plenty of ices. Delta-v to get there from Earth is high, but solar sails are more effective for trips to and from it. And of course, there's plenty of solar power. Its surface gravity is slightly higher than that of Mars, but its gravity well is smaller and the lack of an atmosphere makes use of rocket landings easier (the atmosphere of Mars is thin enough that powered landings are needed for large payloads, but getting stable operation from rockets pointed into a hypersonic airstream is...difficult). The worst difficulty is solar radiation on the trips to and from it.icekatze wrote:That is very cool, looking at the photos Messenger sent back from its flybys, it got me thinking about the feasibility of building facilities on a close, tide locked planet like Mercury. With all those craters, there are lots of places that are covered in shadow even as you move away from the terminator.
Indeed...it reaches Vesta this July and stays for a year. I'm particularly interested in Ceres (which is almost a scale model of a planet and may have an ocean of liquid water), which it won't reach until February 2015...but we're finally getting a close look at two of the largest asteroid belt objects!icekatze wrote:(The mission that I'm following with lots of enthusiasm is the Dawn mission. I know Vesta doesn't have a huge gravity well, but I still think it is cool that the probe is going to go into orbit and then break orbit again before moving onto its next target)
I thought that the surface gravity and the size of the gravity well would be related. how is that possible?Mjolnir wrote:Its surface gravity is slightly higher than that of Mars, but its gravity well is smaller
Well I knew about that "moon" but didn't actually knew the name. What amazing with that is if there a liquid ocean there the possibility of microscopic life form if not well... there water. To bad there is no petroleum there or our space exploration would be on turboicekatze wrote: Ceres really is the big prize, honestly I'm amazed by how few people even know of its existence. Even if Ceres doesn't have liquid water, it almost certainly has water in the form of ice.
Mercury has less mass but notably higher density...more of it is iron rather than rock. Saturn has just over 1 g of "surface" gravity despite having 95 times the mass of Earth. Neptune has slightly higher surface gravity than Saturn, about 1.1 g, despite only having 17 times the mass of Earth...it's got more ices and less hydrogen and helium.Karst45 wrote:I thought that the surface gravity and the size of the gravity well would be related. how is that possible?
Ceres isn't a moon, it's a dwarf planet, recently upgraded from "asteroid". I suspect you're thinking of Europa, though Ganymede and Callisto (around Jupiter) are also thought to be decent candidates for liquid oceans, and possibly Titan (a moon of Saturn).Karst45 wrote:Well I knew about that "moon" but didn't actually knew the name. What amazing with that is if there a liquid ocean there the possibility of microscopic life form if not well... there water. To bad there is no petroleum there or our space exploration would be on turbo ;)
I think titan was the planet i mistook for Ceres.Mjolnir wrote:Ceres isn't a moon, it's a dwarf planet, recently upgraded from "asteroid". I suspect you're thinking of Europa, though Ganymede and Callisto (around Jupiter) are also thought to be decent candidates for liquid oceans, and possibly Titan (a moon of Saturn).
Mass is just mass. The attribute of matter measured on a balance. Gravity is proportional to mass and inversely proportional to the square of distance, higher density planets pack their mass into a smaller volume and put their surfaces at a shorter distance from their mass.Karst45 wrote:I think ill have to retake class on space body, mass isnt the "gross weight without the gravity effect? thus would include the density? Or is mass, in this case, a synonym of "planet size"
Titan's a moon. ;)Karst45 wrote:I think titan was the planet i mistook for Ceres.
Which one? And they were all at least mentioned in my science classes...Karst45 wrote:From the Wiki we discovered it in the early 1800. why isnt it studied in basic astronomy? we learn about all the other planet (i wont give a number cause they kind of changed all that 2-3 year ago so i don't know what number is true now) why not talk about this one?
Well Ceres.Mjolnir wrote:Which one? And they were all at least mentioned in my science classes...Karst45 wrote:From the Wiki we discovered it in the early 1800. why isnt it studied in basic astronomy? we learn about all the other planet (i wont give a number cause they kind of changed all that 2-3 year ago so i don't know what number is true now) why not talk about this one?
what you dont have cyber eyes yet? Poke your eyes out and get upgraded now!Trantor wrote:Live view from earth:
About 40 minutes after sunset, to the west.
Now we just need eyes with better resolution.