Telescopes on Earth can tell us a lot, but some questions can only be answered by going there — or by putting a telescope above the atmosphere. Missions come in a handful of basic types. Each step up the list gets you closer to the answer, but costs more, takes longer, and carries more risk.
Six ways to explore, from quick and cheap to slow and ambitious. Click each one.
Every successful mission is built backward from a science question. The question decides what has to be measured, the measurements decide which instruments go on board, and the instruments decide what kind of spacecraft can carry them. Many of these tools are ones you already know from this course:
| Instrument | What it measures | You've seen the idea in… |
|---|---|---|
| Cameras | Shape, color, texture, and change over time | Every image in this course |
| Spectrometers | Composition, from the fingerprints in light | Activity 4.1.1 (spectral lines) |
| Mass spectrometers | Exactly which molecules are in a gas or sample | Cassini in Enceladus's plumes |
| Magnetometers | Magnetic fields — including clues to hidden oceans | Galileo at Europa |
| Radar | What lies below ice or soil | Europa Clipper |
| Drills and sample arms | Material from below the surface | Curiosity and Perseverance |
| Telescope spectrographs | Gases in a distant planet's atmosphere | Activity 6.1.1 (transits) |
Mission designers start with a question, not a gadget. Pick a question to see what it takes to answer it.
Mars has been the search's testing ground. In 1976, the two Viking landers scooped up soil and ran experiments designed to detect living microbes. One experiment gave a result that looked like life. But another found no organic molecules at all, and most scientists concluded that unusual soil chemistry, not life, caused the signal. The lesson stuck: a single experiment can mislead you.
So NASA changed strategy: "follow the water." Instead of hunting for life directly, missions first looked for places that could once have supported it. The rovers Spirit and Opportunity (2004) found rocks that had formed in water. Curiosity (2012) showed that Gale Crater once held a lake that would have been habitable, and found organic molecules in its ancient mudstone. Perseverance (2021) is exploring an ancient river delta and sealing the most promising rock samples in tubes, so that a future mission could return them to labs on Earth.
The outer Solar System turned out to be full of surprises. Galileo revealed Europa's ocean; Cassinifound Enceladus's plumes and landed the Huygens probe on Titan. Now a new wave is on the way: Europa Clipper (launched 2024, arriving 2030), Europe's JUICE (launched 2023, arriving 2031), and Dragonfly, a rotorcraft set to launch for Titan in 2028. Beyond the Solar System, space telescopes have taken over: Kepler and TESS find the planets, and the James Webb Space Telescope reads their atmospheres.
Fifty years of the search, and what's coming next. Click a mission.
Space agencies receive far more mission ideas than they can fund. The ones that get picked usually have:
| Ingredient | What reviewers look for |
|---|---|
| A sharp question | Not "learn about Europa," but "does Europa's ocean have the chemical energy life needs?" |
| The right instruments | Every instrument earns its place by answering part of the question |
| The right mission type | No more complex than it needs to be — every step up adds cost and risk |
| A plan for surprises | What counts as success, and what results would change the plan |
| Realistic trade-offs | Travel time, power (solar panels fade far from the Sun), and budget |