Raluca Rufu

Southwest Research Institute · Planetary Science Directorate

The hypothesis of lunar origin by a single giant impact can explain some aspects of the Earth-Moon system. However, it is difficult to reconcile giant impact models with the compositional similarity of the Earth and Moon without violating angular momentum constraints. Furthermore, successful giant impact scenarios require very specific conditions s...

The Neptunian satellite system is unusual. The major satellites of Jupiter, Saturn, and Uranus are all in prograde, low-inclination orbits. Neptune on the other hand, has the fewest satellites, and most of the system's mass is within one irregular satellite, Triton. Triton was most likely captured by Neptune and destroyed the primordial regular sat...

A high‐angular momentum giant impact with the Earth can produce a Moon with a silicate isotopic composition nearly identical to that of Earth's mantle, consistent with observations of terrestrial and lunar rocks. However, such an event requires subsequent angular momentum removal for consistency with the current Earth‐Moon system. The early Moon ma...

Forming the Moon by a high‐angular momentum impact may explain the Earth‐Moon isotopic similarities; however, the post‐impact angular momentum needs to be reduced by a factor of 2 or more to the current value (1 LEM) after the Moon forms. Capture into the evection resonance, occurring when the lunar perigee precession period equals 1 year, could re...

The origin of the Uranian satellite system remains uncertain. The four major satellites have nearly circular, coplanar orbits, and the ratio of the satellite system to planetary mass resembles Jupiter’s satellite system, suggesting the Uranian system was similarly formed within a disk produced by gas coaccretion. However, Uranus is a retrograde rot...

As the Moon migrated away from Earth, it experienced a major spin axis reorientation. Permanently shadowed regions (PSRs), which are thought to have trapped ices and are a main focus of lunar exploration, appeared and grew after this (Cassini state) transition and are often younger than their host craters. Here, we calculate the lunar spin axis ori...

The geodynamics of Earth and Venus operate in strikingly distinct ways, in spite of their similar size and bulk density, resulting in Venus’s absence of plate tectonics and young surface age (0.2–1 billion years). Venus’s geophysical models have sought to explain these observations by invoking either stagnant lid tectonics and protracted volcanic r...

The origin of the Uranian satellite system remains uncertain. The four major satellites have nearly circular, co-planar orbits and the ratio of the satellite system and planetary mass resembles Jupiter's satellite system, suggesting the Uranian system was similarly formed within a disk produced by gas co-accretion. However, Uranus is a retrograde r...

Impacts between planetary-sized bodies can explain the origin of satellites orbiting large ($R>500$~km) trans-Neptunian objects. Their water rich composition, along with the complex phase diagram of water, make it important to accurately model the wide range of thermodynamic conditions material experiences during an impact event and in the debris d...

Impacts between planetary-sized bodies can explain the origin of satellites orbiting large (R>500 km) trans-Neptunian objects. Their water rich composition, along with the complex phase diagram of water, make it important to accurately model the wide range of thermodynamic conditions material experiences during an impact event and in the debris dis...

The Earth-Moon system is unusual in several respects. The Moon is roughly 1/4 the radius of the Earth - a larger satellite-to-planet size ratio than all known satellites other than Pluto's Charon. The Moon has a tiny core, perhaps with only ~1% of its mass, in contrast to Earth whose core contains nearly 30% of its mass. The Earth-Moon system has a...

A high-angular momentum giant impact with the Earth can produce a Moon with a silicate isotopic composition nearly identical to that of Earth's mantle, consistent with observations of terrestrial and lunar rocks. However, such an event requires subsequent angular momentum removal for consistency with the current Earth-Moon system. The early Moon ma...

Current lunar origin scenarios suggest that Earth's Moon may have resulted from the merger of two (or more) smaller moonlets. Dynamical studies of multiple moons find that these satellite systems are not stable, resulting in moonlet collision or loss of one or more of the moonlets. We perform Smoothed Particle Hydrodynamic (SPH) impact simulations...

The evection resonance can remove angular momentum from the Earth-Moon system, transferring it to the Earth’s orbit. However, previous studies have found contradicting outcomes (e.g., early vs. late resonance escape), and varied angular momentum (AM) removal efficiency for different tidal models. To explore the origin of such differences and to ass...

The evection resonance in the Earth-Moon system was proposed as a mechanism to remove angular momentum. However, previous studies have found contradicting outcomes (e.g., early/late resonance escape), and angular momentum removal efficiency varies among different tidal models. In order to reconcile these differences and assess the robustness of the...

Earth’s Moon shows indications that it may have resulted from a merger of several smaller moonlets [1,2,3]. We perform Smoothed Particle Hydrodynamic (SPH) impact simulations of two orbiting moonlets inside the planetary gravitational potential and find that the classical outcome of two bodies in free space is altered as erosive mass loss is more s...

Earth’s Moon shows indications that it may have resulted from a merger of several smaller moonlets. We perform Smoothed Particle Hydrodynamic (SPH) impact simulations of two orbiting moonlets inside the planetary gravitational potential and find that the classical outcome of two bodies in free space is altered as erosive mass loss is more significa...

Impacts between two orbiting satellites is a natural consequence of Moon formation. Mergers between moonlets are especially important for the newly proposed multiple-impact hypothesis as these moonlets formed from different debris disks merge together to form the final Moon. However, this process is relevant also for the canonical giant impact, as...

We investigate aspects of the multiple impact hypothesis for Moon's formation, whereby the proto-Earth suffers successive collisions, each forming a debris disk that accretes to form a moonlet. The moonlets tidally advance outward, and potentially coalesce to form the Moon. In addressing the fundamental problem of the Moon's formation, we consider...

In order to evaluate the possibility of forming the Moon from a merger of multiple moonlets, we investigate less massive impactors than previously considered.