The final point made in the previous Crash Course video — that comets may have delivered the key ingredients of life to Earth — is profound. It’s one of the main reasons we’ve invested so heavily in recent decades in exploring comets and asteroids, which are chemically and physically similar. Let’s spend a little more time looking at what we’ve learned from these missions and what questions still drive them today.
Rosetta and Philae — Unlocking the secrets of a comet
The Rosetta mission, launched by the European Space Agency, was the first to orbit and land on a comet — 67P/Churyumov–Gerasimenko. The goal was simple but revolutionary: determine what comets are made of and whether they could have helped spark life on Earth.
In the first video below, Rosetta scientists discuss that very question — “Did comets bring life to Earth?” As you watch, note how they describe the importance of measuring the chemical makeup of comet 67P and comparing it with material found on Earth.
In the second clip, Rosetta team members explain what they hoped to discover by sampling dust and gas from the comet. Pay attention to how those measurements test ideas about the Solar System’s earliest chemistry.
Rosetta’s findings were remarkable: it detected a variety of organic molecules, including amino-acid precursors and phosphorus, but found that the water on 67P has a different isotopic signature from Earth’s oceans — suggesting that asteroids, not comets, may have supplied most of our planet’s water. Its tiny lander Philae also gave us dramatic close-up footage of the comet’s rugged surface and jets of gas streaming into space. In the following video, you’ll learn about three important things Rosetta taught us about Comet 67P — including whether we think comets like it were a primary source of water on Earth.
OSIRIS-REx — Sampling a near-Earth asteroid
Asteroids preserve the same primitive materials as comets but are easier to reach. NASA’s OSIRIS-REx mission launched in 2016, arrived at the carbon-rich asteroid Bennu in 2018, and successfully collected a sample on October 20 2020. That sample was delivered to Earth in September 2023 — the largest pristine sample of asteroid material ever returned.
The next short video explains why Bennu was chosen from among hundreds of thousands of known asteroids. As you watch, listen for the criteria scientists used: composition, accessibility, and potential to preserve organics and hydrated minerals.
In addition to tracing life’s ingredients, OSIRIS-REx has other scientific and practical goals. The next video introduces the Yarkovsky effect — a small but steady force that sunlight exerts on spinning asteroids. Over time, this can slowly change their orbits, occasionally bringing them close to Earth.
Now that you understand Bennu’s hazards and importance, watch how OSIRIS-REx collected its sample using the “TAGSAM” device — a robotic arm that briefly touched the surface, stirred up dust, and captured it for return to Earth.
Analyses of the returned material are now underway, revealing abundant carbon and water-bearing minerals — direct evidence that asteroids like Bennu contained the raw materials for life. The spacecraft itself has been renamed OSIRIS-APEX and is on course for a rendezvous with the near-Earth asteroid Apophis during its close approach in 2029.
Beyond Bennu — New missions extending the story
JAXA’s Hayabusa2 mission returned samples from the asteroid Ryugu in 2020, confirming that water-altered minerals and amino acids were widespread in the early Solar System. Together, the Hayabusa2 and OSIRIS-REx samples let scientists cross-check their results and build a clearer picture of how organics were distributed.
NASA’s Lucy mission (launched 2021) is now on its way to explore the Trojan asteroids that share Jupiter’s orbit. These ancient bodies may have formed in different parts of the Solar System and were trapped by Jupiter’s gravity during planetary migration, offering a “fossil record” of early Solar System dynamics.
NASA’s Psyche mission (launched 2023) is headed to the metallic asteroid 16 Psyche — possibly the exposed core of an early protoplanet. By studying Psyche’s metal content and magnetic history, scientists hope to learn how planetary cores formed and differentiated billions of years ago.
Why these missions matter
- Origin of life: Determine whether water and organics arrived on Earth via comets, asteroids, or both.
- Planetary formation: Reveal how solids and ices combined and evolved in the early Solar System.
- Solar System dynamics: Test models of planetary migration and small-body evolution.
- Future exploration: Prepare for possible asteroid resource use and long-term impact prevention.
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