Art Project 2 Instructions To get started:
While keeping this Instructions page open, go ahead and open up a second browser window or tab, for the "Art Project 2 Lab Journal" quiz/form.
You will be collecting information about a known extrasolar planet and its host star in "Phase 1" that needs to be recorded near the top of that form. Further down, you will fill in some more details and answer a few questions as you complete that and "Phase 2," and then answer some more questions based on your experience in "Phase 3."
Unlike in Art Project 1, where the different project phases had different due dates, here you can do the whole thing all at once. Having the "Lab Journal" quiz/form already open as you read and work down through these Instructions should help smooth out the process overall.
Let us get started with...
Phase 1 — Find a Planet!
For this portion of the project we will use the "NASA's Eyes" app — available either online to run in your web browser, or as a free downloadable stand-alone program, at the following links:
in-browser version: https://exoplanets.nasa.gov/eyes-on-exoplanets/ (链接 到外部网站。)
stand-alone app: https://eyes.nasa.gov/ (链接到外部网站。)
The two versions present the same general information, although the formatting is slightly different. The performance (speed / smoothness) and visual quality is generally better in the stand-alone program, although the web-based version has the advantage of not needing to deal with downloading and installing a new piece of software on your computer. You may use either for this project.
If you decide to get the stand-alone app version, note that it has several "modes" — all of which are cool, of course — but for this project we will specifically be using the "Eyes on Exoplanets" one (open the app, and choose "Eyes on Exoplanets," on the far right side of the main menu screen; there may be a little pop-up that asks whether to use the app in full-screen mode or not, and it does not matter which you choose).
A short introductory sequence will play, showing an overview of the data set of stars in the Sun's neighborhood, and which of those have been identified as having planets.
After the introduction plays through, you can click-and-drag to move the view around, and look around at the stars that have had planets detected around them (the stars with 8-pointed star icons, instead of just tiny dots). You can scroll up or down to zoom in and out (or use the slider on the far right side of the window in the stand-alone app).
Depending on how closely zoomed in on the Sun, or how far outward you are looking from, you may notice a couple of distinct "ray-shaped" or clustered regions of the galaxy in which a large number of planets have been detected around stars in those directions. These are data sets from specific dedicated planet-detection surveys — including, especially, the Kepler mission you learned about in Unit 3 of the astronomy video game. There is nothing necessarily "special" about those specific directions in the galaxy that suggests there are more planets formed around stars there; it is simply a result of the planet detection surveys concentrating their observations in those directions. One could imagine the formation of planets around stars in any given other direction as well — although as you learn in Unit 4, there are vastly more stars within the disk plane of our Milky Way galaxy than outside of it.
You can hover your mouse over any of these stars to see the star's name (or catalog entry number, in a lot of cases), how many planets have so far been discovered around it, and how far that star is from our Solar System.
There are a great many to choose from. NASA's Eyes also has a certain few they highlight of particular interest; if you are using the web-browser-based version of it, then you can click "Browse Planets" at the top right to look over
some; if you are using the downloaded version, try clicking the little spark-outlined "!" icon along the middle of the top of the window.
Click on a star to zoom in on it.
TIP: Especially if you are using the downloaded stand-alone version of NASA's Eyes, you may want to go ahead at this point and write down the name of the star you clicked on, since that program will occasionally reset itself back to the initial "start up" view, or enter a "highlights / tour" mode on its own, if left idle for a few minutes. You can prevent this by just interacting with the star or planet, clicking a button, etc. now and then to keep it focused on your chosen target.
Making a note at least of the name of a star you are interested in will help you quickly track it down again, later, using the Search function (magnifying glass icon, along the top) in either the app or in the web browser version.
You can enter this star name in the first question blank of the Art Project 2 Lab Journal.
You can click on the "Star" button in the lower right (if using the browser version — or the "Star View" button on the left in the stand-alone version) and, below that, see a comparison between your target star and our Sun; or for the stand-alone version, a pop-up window on the left will tell you a few things about the star itself.
That information on the star may include...
Name o ... which may be a stellar catalog number entry in most cases. Recall that a great
majority of stars are fainter than those we can readily see with the naked eye from Earth.
Distance from Earth o in light-years
Visibility o whether this star is possibly visible to the naked eye, from Earth (depending, of course,
on the sky conditions at a given location on Earth) Number of Planets
o note: this is just the number so far detected — not necessarily all of them that might be there! (further discussion on that point, below)
Star Type o just like the spectral types we described in Unit 3; i.e., "O B A F G K M"
o This is a function of brightness, but on a logarithmic scale; a lower number on this scale means a brighter light source. Recall the "Inverse-Square Law," and that we can derive an estimate of the star's actual luminosity (relative to our Sun's) if we also have an estimate of its distance from us (which NASA's Eyesalso provides).
o The web version of NASA's Eyes does not show this information, or in some cases it may not be well defined or known, but you can take a look at the video game's companion "Encyclopedia" page on Stellar Mass (链接到外部网站。) for an idea of what the star's luminosity (not brightness) may be, based on type.
Mass o relative to our Sun's o The web version of NASA's Eyes does not show this information, or in some cases it
may not be known, but you can take a look at the video game's companion "Encyclopedia" page on Stellar Mass (链接到外部网站。)for an idea of what the star's mass may be, based on type.
You can zoom out by scrolling to get away from the star close-up and see the planet(s) orbiting around it; alternatively, in the web version click the "System" button in the lower-right corner, or the "Planetary System View" button on the left in the stand-alone app.
In the stand-alone program, to slow down the rate at which the planets are shown moving in their displayed orbits, use the slider at the center/bottom of the window. If you slide the slider bar to the center, it will pause; alternatively, you can click the "real rate" button and it should nearly stop the planet motion. This makes it much easier to click on an individual planet to view its information, later.
You can click "Compare with our Solar System" (lower-right in the web version, or middle of the left side in the stand-alone version) to see about how large the planet(s) orbits are estimated to be, compared to the orbital distances of our Solar System's planets about the Sun. For the great many of these stars which are lower mass than our Sun, you may be surprised at first at just how close many planets orbit — multiple planets within the orbit of Mercury, for instance. Some of the reasons for this being a common observation — not so surprisingly, in retrospect — are described in more detail, below.
You can also click the "Habitable Zone" button to see a blue-shaded region around the star that estimates the range of orbital distances which may allow for liquid water on a planet's surface, should it orbit within that region. This is based on a pretty simple calculation that does not include some factors that
may contribute to this region being larger or smaller. For instance, our planet Earth might well be a little too cold for liquid water if it were not for having an atmosphere to help retain heat at the surface via the "greenhouse effect"; on the other hand, Venus' "runaway greenhouse effect" has rendered what might otherwise have been a habitable planet into a super-hot wasteland.
The roughly-estimated habitable zone overlay may not necessarily display for all stars, since it depends on having sufficient data on the star to make those calculations.
Click on a planet to view some information on it, which may include...
Name Planet type
o Bear in mind that this is a "first guess" based on the limited physical characteristics we can measure, combined with some comparison to planets in our Solar System.
o Some of these "nicknames" for planet types — "Hot Jupiter," "Neptune-like," "Super Earth," etc. — just come from best guesses based on the specifics of the star & planet, and comparisons to what we have in our Solar System. A "hot Jupiter," for instance, is something that may be Jupiter-sized (or even bigger) that is closer to the star than Jupiter is to our Sun. A "Super Earth" might be something that is ... sort of around Earth-sized — a little bigger, but quite so large as to enter into the class of a gas giant or "Neptune"-like. A rocky planet, of course, is probably just a rocky planet — perhaps like Mercury, or Earth's Moon, but could still also be something like Mars or Venus, or... even Earth (in absence of knowledge about an atmosphere). Again the point is: the "planet type" given here is kind of an initial guess, and not necessarily any sure thing.
Discovery Date Planet's Mass, if known (may be an estimate)
o May be expressed in numbers of Earth or Jupiter masses (recall that Jupiter's mass is
about 318 × Earth's) Planet's Radius, if known (may be an estimate)
o May be expressed in numbers of Earth or Jupiter radii (recall that Jupiter's radius is
about 11 × Earth's) Orbital radius
o Expressed in Astronomical Units ("AU") Orbital period
o In hours, Earth days, or Earth years, etc. Eccentricity
o Recall that this is a measure of how elongated (elliptical) the planet's orbit is; a value of 0 corresponds to a circular orbit, and gets closer to 1 the more elongated it is (like we see for comets, but also for some planets in other star systems)
Method of detection o Usually either "radial velocity" or "transit," although a growing number are found
through "micro-lensing" as well
You may search around in NASA's Eyes for as long as you like, until you find a planet you find interesting. For this project you are not required to find a specific planet, or a star or planet of any particular type. NASA's Eyes updates every so often with a few "featured" planets (look for the "Browse Planets" option at the top of the web version, or in the stand-alone app try clicking either the telescope dome icon for "latest discoveries" or the exclamation-point/spark icon for "extreme planets" and then one of the numbers that appears along the bottom of the window).
Once you have found a star and a planet that you want to work with further, then go to the "Art Project 2 Lab Journal" quiz/form page (again, probably most convenient if this were opened at the start and then kept open in another window or tab throughout your work on this project). Fill in the upper portions of it (the "Phase 1" section) with all the information gathered from NASA's Eyes.
There are also a couple of short essay-type questions at the end of this section, that should only take a couple minutes to fill in. You can use these spaces to note what motivated or inspired your selections of a particular star and planet in NASA's Eyes here in "Phase 1."
Next: Let us pause, here, to review some of the relevant science involved in all this ...
1. What can we tell (or begin to guess) about a star or planet, based on just a couple measurements like a spectrum, or seeing a periodic partial drop in brightness or a little wobble?
From topics covered in Units 1 & 3: if you have a determination of a star's spectral type ("O, B, A, F, G, K, or M") — basically a more
in-depth measurement of its "color" — then you can estimate its temperature (also, its chemical make-up; more on that, below).
We can estimate the star's distance from Earth using the parallax method, like you learned in Unit 3. NASA's Eyes supplies some of this information. If you can measure how bright the star looks (again, often noted in the aforementioned "magnitude" scale), then you can combine that with the parallax-derived distance and determine its actual luminosity.
The star's luminosity and temperature can help you estimate how large the habitable zone around it is — or just generally make a very basic guess at how hot or cold the surface of a planet would be at a given distance away from it (that is, before figuring in some potential complicating factors like atmospheres, greenhouse effects, tidal heating, other internal heat sources, etc.).
Also, recall from this article from Art Project 1 that the star's temperature (or the resulting dominant colors of light from it) will affect how strongly colored the scene may be.
o As for what this can suggest about the planets, themselves...
Usually the best-defined measurement we have, due to the nature of either the radial velocity or the transit method, is of the planet's orbital period. Even if we cannot see the planet itself directly, we can see its influences on the star, and how often those changes occur. The radial velocity method gives us an orbital period since we can see how often the star moves one way or another due to the planet's gravitational influence. The transit method looks instead for little "micro-eclipses," and we can derive an orbital period for the planet based on how often those eclipses occur.
Once you have the orbital period, you can work out the orbital distance, too. This comes from Kepler's 3rd Law,
again, P2=a3 — however, with adjustments that take into account that the other star probably has a different mass than our Sun (an assumption that is built into that simplified form of Kepler's 3rd Law you are most familiar with).
If you can determine the planet's orbiting distance from the star, then you can work out a better informed "guess" as to what conditions may be like on that planet — again, based on some broad assumptions — such as...
Surface temperature: If the orbital distance is small, and/or the star is very hot or
luminous, then you might expect a very hot planet's surface. If the orbital distance is large, and/or the star is cool or dim,
then you might expect a very cold planet's surface. Whether NASA's Eyes displays the planet's orbit as lying in
the star's estimated "Habitable Zone," too, can figure into your guess at the surface conditions.
Surface temperature calculations depend on the overall color or reflectivity of the planet's surface, as well — something we cannot necessarily determine, remotely. So there is plenty of guesswork involved, here.
How bright the sky is, and/or how brightly lit up the ground is: Some of this will depend on what the planet is made of, of
course — and there is a lot of that we do not know (and may not know for a while, until detector technologies and methods improve), so here you might take more "artistic license" in what you imagine the surface conditions will be.
But, at least in general a dim star and/or one that is far away is going to give you a pretty dark planet; or a bright star or one close by will give you a planet surface that is likely very bright. If the planet has a substantial atmosphere, it might mean a bright daytime sky. Without an atmosphere, it may just be dimly or brightly lit ground, while you can still look up and see stars scattered around in an otherwise nearly-black sky.
Composition: If you remember the lesson near the end of Unit 2 about how
the Solar System formed, then you can make some additional guesses about what the planet might be made of, based on how close or far away it is from its parent star.
Think of how the innermost planets in our Solar System are dominated by metallic or rocky materials, then progress to more carbon-rich, or gaseous or icy (water ice or other frozen chemical species) materials as you get towards the outer regions.
2. How can we know a planet's mass, or size — but not necessarily both?
This is generally because the method of detection gives you an observation of one or the other property, not really both — although both methods can be used on the same star (often a radial velocity study to follow up a transit detection).
The "radial velocity" method relies on being able to detect the gravitational tug of a planet on its parent star, so the strength of that tug gives you an idea of the planet's mass relative to the star's; the star's mass itself, though, may also be just an estimate (but can be based, with some assumptions, from its spectral type). Since we do not necessarily know the view-angle orientation (from our point of view on Earth) of the planetary system in radial-velocity detections, our determination of the planets' masses are sometimes averages within possible boundary values.
In the "transit" method, we can see the fraction decrease in the light detected from the star (recall from Unit 3's discussion that it is like observing a miniature partial eclipse). How much of a dip in the light tells us how large the planet is compared to the star, letting us estimate its size — but not its mass.
Since a planet detected by the transit method is in a system with an edge-on (or nearly edge-on) angular orientation from our perspective, we can do follow-up studies using the radial-velocity method and determine better estimated masses of those planets. Masses, taken in addition to the size estimates we got from the transit, can lead to... Density: If you have a good estimate of both the physical size
and mass of something, then you can use the
formula, density=massvolume (recalling that for a
sphere, volume=43πR3), and begin to make a better guess at what the planet might be made of — metal, rock, ice, gaseous materials, etc. This still depends on a number of assumptions, of course, but we can support our guesses by referring to examples in our Solar System.
Surface gravity: Recall the application of Newton's Laws like in
Unit 1 — that is, g∝mr2
3. How can we guess what a planet's type is?
This follows from the answers to questions 1 & 2, above; part of it is guessing what a planet might be made of. You can also take into consideration the distance between the planet and the parent star, determined using Kepler's 3rd Law.
More generally — if you think about the examples in our Solar System — even if all you have is an estimate of a very high mass, or a large radius (but not having both), then you might still make a first guess that something is a gas giant.
Alternatively, if you estimate a low mass, and/or a small planet radius, you might guess that something is more like a terrestrial planet. A low-mass object tends to have too-weak surface gravity to gather up and hold on to extended atmospheres of light gases like hydrogen and helium.
If the planet is close in to the star, it may be more likely to be a metallic or rocky object. If it is far away (like outside of the star's expected "habitable zone"), then it may be more likely to be an icy object. Again, you can recall this from the discussion of the formation of the Solar System near the end of Unit 2.
None of these are certain things, however! What we have learned over the last few decades in planetary sciences research is that star & planetary systems can be a lot more dynamic than previously assumed. It is not necessarily the case that for every planetary system the "inner planets" will always be terrestrial, or that the "outer planets" will always be gas giants. Planets and stars interact gravitationally in ways that may cause them to migrate between orbits, switch locations, and so on.
It happens that our Solar System appears to have been "generally stable" for a long time after the planets formed, but other systems may not exhibit the same behavior. Something like a gas giant might start out in an outer orbit and slowly spiral inward, perhaps puffing up as it heats up. A terrestrial planet that started out close to its star may have gravitational interactions with other objects that fling it into an outer orbit. And so on...
4. Why have we not yet found more planets like the ones in our own Solar System?
A quick answer could be: Because planets like those in our Solar System would be very hard to detect, using the level of technology,
time, and resources, etc. we have had available until now, and the precision needed in measurements.
A great many of the earliest detected extrasolar planets were giants — often much more massive than Jupiter — and at close distances to their parent stars. This makes sense: it is much easier to see planets' gravitational tugs on their stars when the planets are both very massive, and are exerting that force up close (which means more strongly) and on a more-rapid time scale.
In the case of transiting planets: there, too, it is easier to see "partial eclipses" when the eclipsing object is larger. So our earliest detections have tended to be of larger objects, not Earth-sized ones or smaller.
For either method (radial velocity or transit), it is also easier to confirm a potential planet detection when you can observe for long enough to see multiple orbital periods (multiple push/pull cycles, or multiple transit events). This is easier when the orbital periods are very short. Our Earth has an orbital period of one year, so you would have to be observing the same star for at least a year — multiple years — to be confident that the little dip in a remote star's light was caused by a transiting planet in a regular orbit and not by some other factor. For other planets in our Solar System with even longer periods, well... to spot such things around other stars could take a very long observing time!
5. What else might we be able to tell about these extrasolar planets — now, or in the near future?
We can return to spectroscopy, here. With fine enough resolution looking at certain light wavelengths of
interest, you might be able to tease out differences between the apparent spectrum of the parent star "by itself" (say, near but not during, a transit) and when the planet is in some other position away from in front of the star and its Earth-facing side is brightly illuminated. In transit observations, if the planet has an extended atmosphere, you could even see the effect of that atmosphere as it absorbs some of the starlight passing through it. This helps you figure out some more of what the planet (or at least its atmosphere) may be made of.
You can also look closely at what the parent star is made of. While stars are primarily hydrogen and helium, the proportions of the
remaining elements (carbon, nitrogen, oxygen, silicon, iron, etc.) may be estimated as well (again, by close studies of lines in the star's absorption spectrum). Since presumably the planets around a star formed from the same initial molecular cloud's mix of gases, dust, elements in different relative amounts, ... the star's specific chemistry can give clues as to what the chemical make-up of its planets may be. You may have planets enriched more or less than our Solar System's members in such things as silicate minerals, carbon-rich minerals, other metals, or gases.
Some current and future planet-detection technologies are getting better at blocking or canceling out the star's light, allowing us to begin to see individual planets directly, but the image resolution is still generally only good enough to get brightness measurements or rough spectra (again, leading to chemical make-up) — the objects are just so faint and far away! Perhaps future telescopes will be able to see finer details like oceans, continents, clouds and so on, instead of just fuzzy dots.
In all, it is worth remembering that this is a very active sector of astronomical observations and astrophysical research, today. The initial science results may yield "dry" light-intensity curves, or measurements of alternating red-&-blue shifts, from which one can abstractly determine the existence of planets, and some of their properties. Scientists and artists can work together to make transform that data into real scenes in which you can imagine yourself exploring a planet firsthand. Such is the primary focus of this project.
So with all that said, now it is time to ...
Phase 2 — Build a Planet!
As summarized, above, there is a surprising lot that you can deduce based on just the few physical factors like those gathered in "Phase 1" — those factors, combined with an amount of background knowledge (especially example worlds from our Solar System).
For this phase of the project our Penn State team has developed another mini-game, wherein you can create a customized world. Moving a step beyond "Art Project 1," however, this time there is the element of "bringing the art to life" in that you can begin to play at exploring this world —
— a world which, it bears repeating, is based on a real place (or at least as much as we know about it so far, as reflected in the NASA's Eyes data set), far away around another star, that we have only just discovered in the last few decades.
You can use the online browser-based version of our software tool, here (note that it may take some time to load, depending on your network speed):
in-browser tool: http://www.personal.psu.edu/jds255/teaching/astro7n/Astro7N_ArtPr oject2_web/index.html (链接到外部网站。)
... or, you can download the Astro7N Art Project 2 stand-alone program at one of the following links:
for macOS: https://psu.box.com/s/e8hppes1acw91ekmxgldsy3hfazqsuab (链 接到外部网站。)
for Windows: https://psu.box.com/s/tqdtw0shxgetrro8ymz9wyd0lmx9dgep ( 链接到外部网站。)
for Linux: https://psu.box.com/s/5kmsj0of7c1evntut41yj9p02nexawum (链 接到外部网站。)
When opened, the stand-alone version may display a menu where you can choose how large a display window to use for the program, and what general visual quality setting you want. A higher resolution and/or quality setting may cause the program to run slower on some computers.
When the program starts, you will see a basic planet in the center of the screen, a default star in the background, a menu block with top "tabs" on the left, and some output text and an "Explore!" button on the right.
By default, the "Star" tab is the initially-active one, on the left-side menu. You can start there, and fill in the following based on data gathered from NASA's Eyes in Phase 1:
Star Name o You can either use the name given in NASA's Eyes, or rename the star yourself to
something else. Star Type
o Enter one of the following, from what was in NASA's Eyes: O, B, A, F, G, K, or M o As soon as you enter one of those letters, you will see both the background star
change and the planet illuminated by that color (also, to varying brightness depending on whether the star's type has a high or low luminosity)
Magnitude o You can enter the value given in NASA's Eyes if there were one — or any other
number here. If you do not know (e.g., if a value were not given in NASA's Eyes), then you can just enter "0." This number does not have to be exactly correct.
o If the NASA's Eyes magnitude number happens to be negative, you can enter "0" here as well.
Mass o You can enter the value given in NASA's Eyes (again, in units of Sun's mass), if there
were one. If you do not know (e.g., if a value were not given in NASA's Eyes), then you can take a look at the Astro 7N video game's companion "Encyclopedia" page on Stellar Mass (链接到外部网站。) and enter any reasonable guess based on the numbers in the table (second column from the left). This number does not have to be exactly correct.
Next, click the "Planet" tab to switch modes in the left-side menu. You can then fill in and choose fill the following:
Planet Name o You can either use the name given in NASA's Eyes, or rename the planet yourself to
something else. Mass
o Enter the number from NASA's Eyes, if one was given, that you previously recorded in Phase 1.
o By default the Planet Builder tool assumes a multiple of Earth masses; if NASA's Eyes specified Jupiter masses instead, be sure to click the "Jupiter" button to the right of the text-entry box.
o If this were unknown, then you can enter any number here — your best guess will do. As a rough guide, ...
Terrestrial, "Rocky" or "Super Earth" planets might have masses from a fraction of, to up a few times, Earth's mass (say, 0.1 up to 10 or so).
Something called "Neptune-like," at least as we are used to them, may have a mass of tens of Earth masses (let's say, 10 – 50 times Earth's mass)
A Jupiter-like planet, at least as we are used to them, are more massive than Neptunes, but maybe only up to about a few tens of times Jupiter's mass; above about 100 Jupiter masses or so, you start getting into the realm of lower stars' masses, so better not to enter values above that.
Radius o Enter the number from NASA's Eyes, if one was given, that you previously recorded in
Phase 1. o By default the Planet Builder tool assumes a multiple of Earth radii; if NASA's
Eyes specified Jupiter radii instead, be sure to click the "Jupiter" button to the right of the text-entry box.
o If this were unknown, then you can enter any number here — your best guess will do. As a rough guide, ... Terrestrial, "Rocky" or "Super Earth" planets might have radii from a fraction of, to
up a couple times, Earth's radius (say, 0.25 up to 2 or 3 or so). Something called "Neptune-like," at least as we are used to them, may have a
radius of a few Earth radii (let's say, 4 – 8 times Earth's radius) A Jupiter-like planet, at least as we are used to them, are larger than Neptunes,
but maybe not much larger than Jupiter is, even if the mass is higher; adding more mass to a Jupiter-like planet may actually cause it to compress smaller. On the other hand, other factors may cause a "Hot Jupiter" to puff out some, so if you are entering a guess on a giant planet maybe only go up to 2 Jupiters or so at the most; beyond that and you get into the realm of the smaller-sized stars.
Orbital Distance— in units of AU o You can enter the value given in NASA's Eyes if there were one — or any other
number here. If you do not know (e.g., if a value were not given in NASA's Eyes), then just enter any guess. This number does not have to be exactly correct.
Orbital Period o You can enter the value given in NASA's Eyes if there were one — or any other
number here. If you do not know (e.g., if a value were not given in NASA's Eyes), then just enter any guess. This number does not have to be exactly correct.
o Check the dropdown menu to the right of the box, and choose Earth days (D), months (M), or years (Y).
Surface Type o You have a few options, here: Rocky, Desert, Volcanic, Smooth Ice, Cracked Ice, and
Gas Giant o You can really feel free to choose any one of them, although from a "physics
argument" some of them may make more sense than others; examples... You might not typically expect an icy world very close to a star — such
as inside the inner boundary of its habitable zone — but that is not to say it is impossible. If an icy planet were close to a star, perhaps it is because it spiraled
in from what was originally an outer orbit, and it is slowly melting or getting vaporized.
A very large and/or very massive planet (anything measured in "Jupiter" units) is probably more likely to be a gas giant than another type.
Atmosphere On/Off, & Type o Again, you have a few options, here. Click/check the button if you want your planet to
have an atmosphere. Or, you can leave it unchecked if you imagine that your planet has no atmosphere. There could be an argument for going any of several ways — no right or wrong choice, here; think of notable objects in our Solar System, everything from densely-clouded Venus, to thinly-covered Mars, Mercury with essentially no atmosphere, ... and then there are hazy Pluto or smoggy Titan, too.
o If you do check the Atmosphere button, a dropdown menu appears — defaulting to a "No clouds" setting. Options include: "No clouds": you can leave the atmosphere on, but there will just be a low/thin
atmosphere "haze" showing up near the horizon in your scene. This may be similar to a place like Mars, Pluto, or another low-mass planet.
"Some clouds": as its name implies, the scene will include a little more substantial an atmosphere and some cloud effects added in.
"Thick clouds": with this setting, the sky will be pretty heavily clouded over and hazy, making the scene more lit up like "daytime" as we are used to on Earth. Background objects like stars, moons, or rings will be hard to see.
Click the "Extras" tab to switch to that third mode in the left-side menu. You can then choose a few more options, including:
Habitable o Your planet, based on what is shown in NASA's Eyes, may lie within your chosen
star's "habitable zone." o Even for planets that are not "habitable" based on distance from their parent star
alone, other factors may make a planet's surface warm enough to have liquid water... atmospheres and corresponding greenhouse effects (like in the case of Earth) tidal heating from a nearby other planet or moon (like in the case of Io or Europa,
around Jupiter) internal heat sources like radioactive elements, and/or just high pressures and
plate tectonics, volcanoes, etc. (like Venus or Earth, and maybe Mars in the past) o Note that "Habitable" does not necessarily mean "Inhabited"; just because liquid
water may exist on the planet's surface, 1) does not mean that it does, and 2) is no guarantee that the surface can support living things
o Regardless of reason, you may click/check this button if you want to switch out your surface type to one that includes a surface ocean, and simulates some simple
vegetation on the land surfaces (note: this replaces your surface type choice from the "Planet" tab, above).
Rings o Click or check this button to add a ring system to your planet — just for fun! o In our Solar System, the gas giants have rings and the terrestrial planets do not (at
least not "substantial" or permanent rings) — but this may not always be the case. Earth, for instance, might have (or have had) a ring, temporarily, in the wake of a large asteroid impact or near-miss by something. A few processes might lead to rings around different types of objects.
Moons o Options include: No moons, 1 moon, 2 moons, or "Many moons." o Again, there are no "correct" answers here, although remember that at least in our
Solar System, the gas giants tend to be the ones with many moons while the terrestrial planets have a few or none.
o An exception of course — somewhat to our surprise, initially — is little icy Pluto, which has five (at least)!
Before going any further, return to the "Lab Journal" and note down what selections (surface type, atmosphere) you made in the planet builder, in the couple of blanks where it asks.
Next, turn your attention — if you have not already — to the panel on the right side of the Art Project 2 "World Builder" program window. Do not click the "Explore!" button, just yet.
You can see the star's luminosity and temperature noted, here, based on what star type you specified earlier.
Below those, you can see an estimated planet's surface temperature calculated as well. This is from a very simplified calculation, based in part on assumptions of how light absorbing/reflecting the planet's surface may be. It is not necessarily accurate, but can give you some idea of what it might be.
If you wish, you can change around some of your entered numbers or options to see what effects they have on the temperature. Major factors are, naturally, things like the star's luminosity and the planet's distance from it. Some surface types may be dark and absorb more light — and heat up — than others. While atmospheres may help retain heat on a planet, bright white clouds might have a partial cooling effect. Think of the difference between wearing black or white clothing on a bright sunny day, or of walking barefoot on either a dark road surface versus light beach sand, and so on.
Make a note of the estimated surface temperature in your "Lab Journal."
Below surface temperature is a calculated surface gravity (using the familiar formula from Newton's Laws). Make a note of this, too, in your "Lab Journal."
Below that, there are a few more short written response questions to answer in your journal, about your customization choices and expectations.
Now, at last, it is time to ...
Phase 3 — Explore a Planet!
Now you can click that shiny "Explore!" button on the upper-right side of the window, and be transported to a little "landing site" on your custom-built world.
Player controls for this part are much as you have used before in the Astro 7N video game.
You can turn the "on-screen help" display on or off by tapping the [H] key. Whether you choose to explore on foot (in a spacesuit), in a land vehicle, or flying in the
ship, use either your arrows or "W-A-S-D" keys to steer or move around. You can switch between modes by tapping the number keys:  for an astronaut in a
spacesuit, on foot;  for a surface rover;  for a spaceship. In the case of the spacesuit, you can look around while walking or standing still by moving
the mouse. If you fly (or fall) too far from the starting location, the game will turn you back towards the
starting point. If you wish to return to the "Builder Mode" to try out something else, just press
the [escape] key. Your previous settings may not be restored, but remember that you can look back up your Lab Journal to see what your previously-entered data and options were.
While exploring, you may take note of how your player reacts to the gravity setting. You may find you can jump higher or not as high as "normal."
There are several more questions for "Phase 3" in your Lab Journal to answer, before submitting it as your Art Project 2.
Please go over it to be sure you have filled in all of the name or data-entry blanks, and answered the several questions in different sections.
There is also a place to upload a screenshot of your custom world. We are interested in seeing what you came up with!
Continue exploring as much as you would like. Be sure to submit your "Lab Journal" with the button at the bottom to get credit for completing this project.
You may of course re-visit NASA's Eyes and the Astro 7N Planet Builder/Explorer program to try out other things.