By Laurence Tognetti, MSc
April 15, 2025
How can we successfully collect and return samples from Mercury and Venus to Earth? This is what a recent study presented at the 56th Lunar and Planetary Science Conference hopes to address as a pair of researchers from the California Institute of Technology (Caltech) discussed how future missions could successfully conduct sample return missions from the two innermost planets in our solar system. This study has the potential to help scientists, engineers, and mission planners better understand new methods for conducting sample returns throughout the solar system, and specifically from hard-to-reach destinations.
Here, Universe Today discusses this incredible research with Teng Ee (Tony) Yap, who is a PhD student at Caltech and lead author of the study, regarding the motivation behind the study, significant takeaways, next steps for developing sample return missions, and the importance of returning samples from Mercury and Venus. Therefore, what was the motivation behind the study?
Yap tells Universe Today. “This study came out of a workshop held by the Keck Institute of Space Studies (KISS) at Caltech on Sample Return across the Solar System, which brought together experts in geo/cosmochemistry, orbital dynamics, mission science, etc. (as well as early career scientists like myself) to discuss the highest priority scientific objectives that can be achieved through sample return from bodies spanning the whole solar system, and what technologies need to be developed for those missions to be feasible.”
For the study, the researchers discussed the pros and cons of obtaining samples from Mercury and Venus, specifically mentioning the absence of meteorites that originate from the inner solar system, as all collected meteorites have originated from beyond the Earth’s orbit, specifically the main asteroid belt, Mars, and the Kuiper Belt. The researchers emphasized that along with the lack of meteorites from the inner solar system comes a lack of knowledge regarding the planetary building materials, such as carbonaceous and non-carbonaceous materials, and what materials could have existed in the inner solar system during its early formation billions of years ago.
Additionally, the researchers made a case for sample returns from both Mercury and Venus by using past and current missions like NASA’s MESSENGER to Mercury, active missions like the European Space Agency’s BepiColombo to Mercury, and proposed future NASA missions like DAVINCI and VERITAS to Venus. Therefore, what are the most significant takeaways from this study?
“We do not have a single sample, in the form of a meteorite, from Mercury and Venus,” Yap tells Universe Today. “The building blocks of both planets are derived from the innermost Solar System, and we need to know what these blocks look like geochemically to better understand the evolution in the early Solar System ~4.6 billion years ago and figure out if they represent the missing component needed to explain the Earth’s composition. A sample return mission to Mercury is possible with the development of nuclear thermal propulsion – it is unclear when this technology will come online’, however. A sample return mission to Venus doesn’t appear to be feasible, even with nuclear propulsion (largely due to its large mass; tough to get down to the surface and back to Earth). Balloon-based technologies (imagine a lab floating in a Venusian cloud layer) are being considered.”
Getting a space mission approved for flight is often a lengthy and time-consuming process taking anywhere from several years to decades to go from a proposal to a fully operational and launch-ready space mission. To facilitate this process, NASA incorporates its Technology Readiness Levels system to gauge each step of development for a mission, including laboratory and real-world demonstrations for all systems and subsystems. Each level often involves countless tests, evaluations, re-designs, more tests, and more evaluations until the spacecraft is finally ready for flight.
For example, while NASA’s Mariner 10 was the first spacecraft to conduct a detailed study of Mercury in 1975, it would be another 23 years before another spacecraft was proposed to travel to the closest planet to the Sun. This is because traveling that close to the Sun is very dangerous to the Sun’s enormous gravity that would pull in any spacecraft traveling too close. Therefore, multiple gravity assists and planetary flybys were utilized to slow a spacecraft to the necessary speeds to orbit Mercury.
The MESSENGER spacecraft was proposed in 1998 and launched in 2004, but didn’t enter Mercury orbit until 2011. Therefore, what are the next steps for developing future missions to return samples from Mercury and Venus, along with what is the importance of returning samples from Mercury and Venus?
Yap tells Universe Today, “Pushing for the development of nuclear propulsion and balloon-based technologies! Getting the community excited about looking ‘in’ towards Mercury and Venus, in addition to looking ‘out’ towards the giant planets and their moons. Strengthening the science case for sample return to those planets (i.e., figuring out how to make the most of, say, 1 gram of rock scraped or drilled from their surfaces).”
Yap continues, “Mercury and Venus have the potential to solve a major and longstanding problem in the field of cosmochemistry: tracing the building blocks of the Earth. Ironically, we don’t know how to ‘build’ the Earth from materials we know; there is no mixture of meteorites we know that yields the Earth’s composition.”
How will returned samples from Mercury and Venus help scientists better understand the history of the planets and the solar system in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!