Extra Solar Planets Interactive (135.0K)
Is it possible that the “wiggle” of a star can tell astronomers about worlds in other star systems? Yes, it is, and this Interactive will show you how. When planets orbit a star, they impact the motion of the star, and by observing that motion, astronomers can infer the presence, mass and distance of the planet. Things get more complicated with there are multiple planets. Observe Earth’s impact on the Sun’s motion, and you will understand why Earth-type planets around other stars are hard to detect. Compare that to a “Hot Jupiter” and see how much more readily it can be seen. Then observe the multiple planet system to see how its much more complex interactions are reflected on the graph.

1			51 Pegasi's planet was found by what method in 1995, and why did its discovery create much controverse? Need a Hint?
			A)	It transited its star every 4.23 Earth days, and the dimming of the star's light indicated the planet was as large as its star!
			B)	Its gravity caused its star to wobble back and forth with a 4.2 day period, found by doppler shifts. This indicated the planet, as massive as Jupiter, was not where a Jupiter should be!
			C)	We found it emerged from its star's glare every 2.1 days, much as Mercury is seen in morning or evening twilight. It was much brighter than expected.
			D)	We found radio signals were coming from it, and they were being doppler shifted back and forth every 4.2 days. Jupiter is not this strong a radio source.

Nu Andromedae has three jovian type planets orbiting around it. Let's use the orbit of the innermost, and Newton's revision of Kepler's third law, to weigh its star.

2			Using Kepler's third law relationships, how massive is Nu Andromedae if its innermost planet orbits it at .06 AU every 4.6 days? Need a Hint?
			A)	27 solar masses.
			B)	8 solar masses.
			C)	1.4 solar masses.
			D)	.8 solar masses

While in the previous question, we used the inner most jovian of Nu Andromedae to weigh the star, now let's look at the distances of the two outer jovians that orbit this star, with comparisions to our solar system.

3			The two outer jovians have distances of 2.0 adn 4.1 A.U. from Nu Andromedae. What does this bring to mind closer to home? Need a Hint?
			A)	Mars orbits at about a third of Jupiter's distance from the Sun.
			B)	Saturn orbits at twice Jupiter's distance from the Sun.
			C)	Pluto is in a 3:2 orbital resonance with Neptune.
			D)	Mercury has a 3:2 spin-orbit resonance.

On June 8, 2004, the planet Venus transited the Sun. We now know of several cases where hot jupiters also pass in front of their stars, and even amateurs with photometers are helping monitor hundreds of stars for such recurrent dimmings. What can they tell us about the planets involved?

4			A star like our Sun has a jovian transiting its disk every 5.7 days, and the star dims by 9% every time this occurs. How large must this jovian be, given that the diameter of Jupiter is about 1/10 the Sun's diameter? Need a Hint?
			A)	This object must be almost the same size as Jupiter, which would block 10% of our Sun's light.
			B)	This object is nine times larger in diameter than Jupiter, which would block only 1% of our Sun.
			C)	This planet is three times smaller in diameter than Jupiter.
			D)	This planet is about three times larger in diameter than Jupiter.

In 1995, the first planet orbitting another star was discovered, and since then, the count of other solar systems has passed one hundred and growing daily. But to date all are comparable to at least Uranus in size. How can we find Earths instead?

5			NASA's Kepler mission is scheduled for launch in 2006, and will photometrically look for transits of even smaller habitable terrestrial type planets, where the dimming will be a tiny fraction of a percent. In relation to systems like ours, what time spans for orbits will Kepler be looking for? Need a Hint?
			A)	No more than six days.
			B)	Between six months and two years.
			C)	Two to twelve years.
			D)	Twelve years and longer.