RESEARCH: PLANETARY RADAR SCIENCES

Planetary Radar Science, a portion of Solar System Astronomy, is essential for probing the physical properties, shapes, and surface features of celestial bodies, as well as for accurately determining their orbits. By using radar signals to map and analyze objects like asteroids, moons, and planets, it enhances our understanding of their evolution and helps assess potential hazards to Earth.

To understand the research we pursue at Florida Space Institute in the context of Planetary Radar Sciences, it is important to know the fundamentals of it.

WHAT IS PLANETARY RADAR?

PLANETARY RADAR

Using planetary radar, scientists study the celestial bodies in our solar system: planets, moons, asteroids, and comets. A powerful beam of radio waves is transmitted in the direction of the target object, and a very small portion of the energy reflected by the target goes back toward the direction of Earth. This weak radio echo is collected, focused, and detected by the radio telescope. The signal is processed and then analyzed to yield information about the surface roughness, composition, size, shape, rotation, and orbit of the target object and potential satellites. While optical images project the target on the plane of sky, radar provides the third dimension with a very high accuracy – both the range and the radial velocity. The world’s most powerful planetary radar system ever built was the Arecibo Observatory in Puerto Rico.

RADAR ASTROMETRY

Since NASA’s near-Earth object observations program started funding Arecibo’s planetary radar program in November 2011, the annual number of radar-observed asteroids increased from less than 20 per year to more than 100. Roughly one half of the targets observed each year are recently discovered near-Earth asteroids (NEAs), which usually have large orbit uncertainties. Radar astrometry is a valuable tool for orbit refinement, providing precise measurements that can allow the target’s orbit to be determined much more accurately, preventing the object from becoming lost and requiring re-discovery in the future. In addition, Doppler and range measurements can increase the orbit predictability window from months or years to decades or centuries and can quickly eliminate impact false alarms with improved of estimates of an asteroid’s orbital elements. In the past, the Arecibo radio telescope has also been used to measure the rotation rates of Mercury and Venus.

PHYSICAL CHARACTERIZATION

Planetary radar systems are powerful tools for post-discovery characterization of near-Earth objects, planets, and moons. In addition to precise line-of-sight velocity and range information, depending on the target’s size and distance, planetary radar is useful for resolving the target’s size, detecting potential satellites, and ultimately resolving the shape and rotation state through inverse modeling efforts. Although comets rarely come close enough to Earth to allow strong enough echoes, when an approaching comet becomes detectable by the planetary radar systems, it is possible to get clues to the size and spin period of the nucleus. Furthermore, radar signals can penetrate through clouds (such as the thick atmospheres on Venus or Titan), or several wavelengths below the regolith surface, providing insight into geologic features hidden from optical wavelengths, and provide clues to the near-surface bulk density or metal content of the target based on its reflectivity at radar wavelengths. Radar polarimetry can give clues to the decimeter-scale surface structure, which is crucial for landing spacecraft. The physical properties obtained with radar are fundamental information to support space missions.

*This information was written by Flaviane Faria Venditta, Research Professor at Florida Space Institute