Radio Science Experiment
Studying the Reflexes of MarsInSight’s Rotation and Interior Structure Experiment, RISE, precisely tracks the location of the lander to determine just how much Mars' North Pole wobbles as it orbits the sun. These observations will provide detailed information on the size of Mars' iron-rich core. They will help determine whether the core is liquid, and which other elements, besides iron, may be present.
- Main Job: RISE tracks the wobble of Mars' North Pole as the sun pushes and pulls it in its orbit. This helps scientists determine the size and composition of Mars' core.
- Location: Two Medium-Gain ‘horn’ Antennas (MGAs) on the lander deck, and an X-band radio transponder and transmitter in the lander's equipment bay, where electronics can be shielded from the harsh, cold conditions of space.
- Mass: About 16 pounds (7.3 kilograms)
- Antennas: 3 pounds (1.4 kilograms)
- Transponder and Transmitter: 9.6 pounds (4.4 kilograms)
- Power: 78 Watts (operated up to one hour per day)
- Volume: 0.7 cubic feet (19.8 liters) total
- Electronics: 0.13 cubic feet (3.8 liters)
- Medium Gain Antennas: 0.57 cubic feet (16 liters)
Did You Know?Earth completes a wobble every 18 Earth years as it is pushed and pulled by the Moon. Mars completes a wobble every one Mars year (two Earth years). RISE will tell us exactly how much Mars wobbles, using the same technology that your smartphone uses to tell you your location.
How It WorksRISE works like a mirror, it reflects a signal sent to the lander from Earth, and reveals the exact location of the InSight lander, and Mars, in space. In doing so, it measures changes in the signal, known as the "Doppler shift.” Scientists can use this information, collected over the course of InSight's mission, to understand just how much Mars wobbles in its orbit. This is key to determining the size of Mars' core, and whether it is liquid or solid.
The Planets are Like Moving Sirens
As a siren approaches, it sounds higher in pitch than when it is moving away. This change in the sound is because of the “Doppler shift” in frequency due to the motion of the vehicle. If you know how the signal changes, you can determine how the vehicle is moving. Scientists can use this phenomena to study the planets. They measure the difference in the original signal sent to RISE from Earth, and the signal that arrives at Earth from RISE. This information tells them how the lander is moving in space, and hence, how Mars wobbles in its orbit.
Tracking Mars' Wobble
We know that Earth wobbles every 18 years as it is pushed and pulled by the Moon. And with measurements from the Viking landers and from Mars Pathfinder, we know that Mars wobbles over one Mars year. But we don't yet know by how much. RISE will reveal exactly how much Mars wobbles.
RISE Tells Us About Mars' Core
How much a planet wobbles depends on what's inside it. A hard-boiled egg spins faster than a raw egg. In the same way, a planet that is liquid at its core will wobble more as it spins, than one that’s solid at its core. Understanding how much Mars wobbles will reveal what its core is like.
Scientists know that Mars has a weak magnetic field in some places on its surface. What we learn about the core from RISE and InSight's heat flow package, HP3, will help them understand why Mars' magnetic field is weak, compared to Earth's.