Neptune

by Heidi Hammel

What I like best about the planet Neptune is that every time you look at it, it's different, so Neptune can be >your< planet. The pictures that would be taken of Neptune would be yours. No one else would have seen the clouds that you see and they'll never be seen again probably. And so that means that the pictures of Neptune you take would be absolutely unique...

One of the biggest surprises when the Voyager spacecraft flew by Neptune was a huge dark spot on the planet, and we called it the Great Dark Spot. We weren't able to see it from Earth because Neptune is the most distant planet from us right now, and it is very hard to see things there. When we looked with the Hubble space telescope last year that Great Dark Spot was gone! It had simply disappeared, it wasn't there anymore, which was a big surprise but, when we looked very, very carefully, we saw a different big, dark spot on the planet, in the northern part of the planet -- the other one was in the South -- so that means Neptune's atmosphere just turned upside down! When we would look at Neptune this time we don't know what we are going to see: there might be a whole, new dark spot and that dark spot would belong to this group, they would have discovered it.

...this big dark spot... is a huge storm, a big hurricane. Apparently the hurricanes on Neptune don't last very long, and one of the things that would be really interesting to know was, how long do they last?

Why are the observations important?

One thing that we all care about is the weather. And we care about the weather on the Earth the most. But what makes weather is gases and clouds. And the reason the weather on the Earth is hard to predict is because we have oceans and continents that interact with our atmosphere. That makes it very hard to predict the weather, as we all know. But if you take a planet like Jupiter or Neptune, you don't have continents and you don't have oceans. All you have is gas. All you have is atmosphere. And therefore it is a lot easier to model the weather on those planets. But it's the same physical process, it's the same kind of thing happening whether it happens on the Earth or whether it happens on Neptune. Therefore, by studying weather on Neptune we learn about weather in general, and that helps us understand the weather on Earth better.

What made me want to become an astronomer anyway?

I think there's two things that I remember from when I was a kid that most interested me in astronomy ...I was not an amateur astronomer as a child. The two things: one is that I used to get car sick, and my parents used to take us on trips a lot in the car and so I had to lie on the back seat being sick, and the only thing I could do was look out the window and see the stars. And so I learned the constellations, I learned what the bright stars were, and so that's what kept me going on those long car trips.

And the second thing I remember, when I was a kid, is going to a planetarium, and they would do a star show about what the stars were looking like and what was "up" -- the planets -- and that was all kind of boring, but then at some point during the show a comet would streak across the sky with flames and a roar that was really loud, and you never knew when it was going to happen, and it was really exciting. And I would go back to the planetarium again and again and again just to wait for that comet to come. And I think I probably picked up a little astronomy along the way when I was doing that.

And then when I got into college I took an astronomy course that was just so much fun. I loved working with telescopes, I loved taking pictures of things, taking data, and I just stuck with it.

How can the Hubble Space Telescope make unique observations of these planets, and how many orbits will it take?

The whole Neptune atmosphere is almost unexplored ...we know so little about it that every picture we take gives us brand-new information. Some of the kinds of things that we could learn from images of Neptune is we could study the cloud motions. We could map out where the bright clouds are and where the dark clouds are, and by comparing those with images we've taken in the past we could see how stable the atmosphere is. People are always concerned about weather, weather on the Earth, weather on Jupiter, and a program like this could tell us what the weather is like on Neptune.

We think the dark clouds are something like hurricanes. They have holes in the center, they are like the eye of the storm, you can see into the deeper part of the atmosphere. The bright clouds, on the other hand, are very high-altitude clouds They are like thunderheads that have bubbled up from deeper down into Neptune to very high altitudes and we can see them at special wavelengths that we pick at these high altitudes.

Three orbits are perfect to look at Neptune, because if you pick the spacing in time between the three orbits you could look at three different thirds of the planet and you could make a complete map of the atmosphere, and so if there is any new dark spot there you'll see it, if there is no dark spot there you'll see that, and you'll be able to map out all the bright spots in three orbits.

Even with one orbit of Space Telescope you can get a picture of Neptune at many different colors, and you can look at the cloud activity on that he misphere of the planet. There will definitely be clouds, every time you look at Neptune we see bright clouds. There definitely will be a dark band in the Southern hemisphere. There may or may not be a "Great Dark Spot". But even with one picture you are guaranteed to see clouds. Now we can compare the clouds that we see in that one picture with pictures we've gotten in the past, and that would tell us if certain bands on the planet, certain latitudes are continuously active on Neptune. We have a hint that may be true, but we need to continue looking to see if that really is true and one orbit will be a very good data point in that study. The reason you need HST to look at Neptune is that it is currently the most distant planet in the solar system. Even though it is a big planet, a gas giant, it is very far away, so, even with the best ground-based telescope you could barely resolve any clouds at all...

What's the best, and worst, thing about working with the Hubble Space Telescope?

The HST is a fabulous instrument... you can't get pictures like this any other way. It's fabulous. I just love working with Hubble ...it's incredible to me that there is a robotic telescope in orbit around the earth, and that you can design a program and send these sequences up and move this telescope around to point anywhere around the sky and do any kind of science and get absolutely fabulous pictures, without the earth's atmosphere in the way. You just can't do this from the ground.

The most difficult thing about HST is that you can't make mistakes. In a ground-based telescope, if you calculate the wrong exposure time and your picture is over-exposed you just take another picture with shorter exposure time, but with Hubble you only get one chance, so you've got to do it right the first time. That means you have to work very, very hard to make sure you have everything completely understood and you can't take chances and that makes it hard to use.

Why is the Internet a unique tool to connect students to real science and real scientists?

I think a project like this is a great way for a student to see how scientists make decisions. It's not as easy as just saying "I want to take a picture". There's a lot of decisions that have to get made, a lot of choices, a lot of compromises. Sometimes you can't do things exactly the way you want to do them, and I think it would be interesting for students to see how that happens, to see how scientists really work on a day-to-day basis.

When the students are looking at the various options they have, whether it's Neptune, Pluto, Jupiter... Uranus, they are going to be asking what's the most interesting thing that I can do? And that's what science is all about. That's what scientists do all the time. They think: I want to study this, what's the best way to do that, what's the right way to make the observation, how can I best use my observing time to answer a question? That's what science is all about, and that's what this project is going to allow the students to do.