Planets in the solar system!

[kingwinner]

1) "The large number of craters on Mercury suggests that Mercury has changed little since the formation of the solar system."

Why? I can't see how these 2 things are related!



2) "1 Venus day is longer than 1 Venus year."

Is the above statement true?
http://www.planetary.org/explore/top...rrestrial.html
From this web site, I found that 1 Venus solar day is 117 Earth days (although one rotation takes 243 days), while its orbit period is 225 days.............




3) "The direction of rotation of Venus is opposite to that of the other planets."
Then, is it true that 'the direction of rotation of Venus is opposite to that of ALL the other planets IN THE SOLAR SYSTEM?', or in other words, Venus' reverse rotation is unique?




4) "Most planets, including the earth, rotate with their axes perpendicular to their orbital planes as they revolve around the sun. The axis of Uranus, however, is almost horizontal to the plane of tis orbit."
How come the earth rotate with its axis perpendicular to its orbital plane around the sun? I was long told that the earth's axis is tilted at 23.5 degrees now......confused......




5) "The following gives the rate of rotation of each planet:
Mercury: 59 days
Venus:-243 days
Earth:23 hr 56 min
...............
Uranus: -17 hr 14 min
Neptune: 16 hr 07 min
Pluto: -6.4 days"

The rates of rotation for each planet is positive except for Venus, Uranus, and Pluto. Venus I can understand, because from the quote in Question 3, I know that Venus has a rotation with direction opposite to the other planets and therefore negative.......but what I can't understand is why Uranus and Pluto also have negative signs?

Can somebody explain? Thanks a million!

[Tormod]

Originally Posted by kingwinner

1) "The large number of craters on Mercury suggests that Mercury has changed little since the formation of the solar system."

Why? I can't see how these 2 things are related!

I think the point is that there has been no geological activity on Mercury - or else there would be fewer visible craters. So while the surface is full of craters, there has been no tectonic activity and possible very little (if any) volcanism.

2) "1 Venus day is longer than 1 Venus year."

Is the above statement true?
http://www.planetary.org/explore/top...rrestrial.html
From this web site, I found that 1 Venus solar day is 117 Earth days (although one rotation takes 243 days), while its orbit period is 225 days.............

I don't understand where that 117 figure comes from. The day is 243 days, as you state (ie, one rotation) while the orbit is 225. So the statement above is true.

3) "The direction of rotation of Venus is opposite to that of the other planets."
Then, is it true that 'the direction of rotation of Venus is opposite to that of ALL the other planets IN THE SOLAR SYSTEM?', or in other words, Venus' reverse rotation is unique?

Opposite to that of all the planets in the solar system.

4) "Most planets, including the earth, rotate with their axes perpendicular to their orbital planes as they revolve around the sun. The axis of Uranus, however, is almost horizontal to the plane of tis orbit."
How come the earth rotate with its axis perpendicular to its orbital plane around the sun? I was long told that the earth's axis is tilted at 23.5 degrees now......confused......

Yes, but 23.5% still means it is only slightly tilted away from the orbital plane, so the statement is correct.

5) "The following gives the rate of rotation of each planet:
Mercury: 59 days
Venus:-243 days
...

I'm not sure I understand this one either.

[lindagarrette]

We know more about Mercury after further analysis of the Mariner 10 data. Seems there has been recent volcanic activity, and water!

http://www.psrd.hawaii.edu/Jan97/MercuryUnveiled.html

[Tormod]

Good link, thanks Linda!

[kingwinner]

3) 5) Prehaps I can answer Q3 and Q5 by myself
"Venus, Uranus, and Pluto have a retrograde rotation, or a rotation that is in the opposite direction from the other planets."
http://64.233.161.104/search?q=cache...+planets&hl=en

So Venus, Uranus, and Pluto all rotates in opposite direction to the other 5 planets...and thus Venus is not the only one...


2) But I thought 1 day is defined by 1 solar day, time between 2 sunrises, so 1 solar day on Venus is 117 solar days on Earth, and 1 revolution is 225 days......the strange thing is I was told by my teacher that 1 Venus day is longer than 1 Venus year..........

[Tormod]

A "day" in this context is the time from noon to noon. 1 solar day on Venus is NOT 117 Earth days, but 243 Earth days. So the day is longer than the year on Venus.

[kingwinner]

Originally Posted by Tormod

A "day" in this context is the time from noon to noon. 1 solar day on Venus is NOT 117 Earth days, but 243 Earth days. So the day is longer than the year on Venus.

But 243 earth days is Venus' period of rotation, this is the sidereal day, I think...1 solar day is defined as from noon to noon

[Tormod]

Yes...noon to noon on the given planet.

[Qfwfq]

I agree with King, one must be the sidereal day. They are both called "day" by astronomers.

[C1ay]

Originally Posted by kingwinner

But 243 earth days is Venus' period of rotation, this is the sidereal day, I think...1 solar day is defined as from noon to noon

Yes and Venus' sidereal orbit period is 224 Earth days thus, it's day is longer than it's year. See orbital parameters here. The sidreal rotation period is listed as a negative since it spins relatively opposite to the Earth's rotation.