Unlocking Cosmic Mysteries: Planetary Remote Sensing Applications and Research Techniques

 

Introduction

Planetary mapping product established by topographic remote sensing is one of the most significant achievements of contemporary technology. Modern planetary remote sensing technology now measures the topography of familiar solid planets/satellites such as Mars and the Moon with sub-meter precision, and its applications extend to the Kuiper Belt of the Solar System. However, due to a lack of fundamental knowledge of planetary remote sensing technology, the general public and even the scientific community often misunderstand these astounding accomplishments. Because of this technical gap, the information that reaches the public is sometimes misleading and makes it difficult for the scientific community to effectively respond to and address this misinformation. Furthermore, the potential for incorrect interpretation of the scientific analysis might increase as planetary research itself increasingly relies on publicly accessible tools and data without a sufficient understanding of the underlying technology.

 

This review intends to provide the research community and personnel involved in planetary geologic and geomorphic studies with the technical foundation of planetary topographic remote sensing. To achieve this, we reviewed the scientific results established over centuries for the topography of each planet/satellite in the Solar System and concisely presented their technical bases. To bridge the interdisciplinary gap in planetary science research, a special emphasis was placed on providing photogrammetric techniques, a key component of remote sensing of planetary topographic remote sensing.

 

Applications of Planetary Remote Sensing

1.  Exploration of Other Planets

 

-   Magellan Venus Radar Mapping Mission (1990-94): Spearheaded by the Max Planck Institute for Solar System Research (MKI), this mission was a watershed moment in planetary remote sensing. It unraveled the hidden facets of Venus's surface through radar remote sensing, yielding highly detailed

topographic maps that provided crucial insights into surface roughness and dielectric properties.

 

2.  Characterizing Planetary Atmospheres

 

-   Mars Global Surveyor (1999-2001): MKI scientists played a pivotal role in the Light Detection and Ranging (LIDAR) experiment aboard NASA's Mars Global Surveyor. By analyzing echoes from CO2 clouds in Mars' polar night, this mission enhanced our understanding of Martian atmospheric dynamics, seasonal variations, and the polar atmosphere's state.

 

3.  Mapping Surface Features

 

-   Mars Color Camera (MCC):Deployed during the Mars Orbiter Mission (Mangalyaan), the MCC captured high-resolution images of the Martian surface. This instrument was instrumental in creating detailed maps of Mars, aiding scientists in the study of topography, surface features, and seasonal changes.

 

-   Cassini Saturn Orbiter: Cassini's radar mapping efforts unveiled the rich tapestry of Saturn's moon Titan, unearthing its lakes, mountains, and diverse geological characteristics. This advanced radar system transformed our comprehension of distant worlds.

 

4.  Searching for Extraterrestrial Life

-   Mars Exploration Rovers (Spirit and Opportunity): These intrepid rovers leveraged remote sensing instruments to scrutinize Martian geology, with a specific focus on discerning the potential habitability of past environments. Their missions have reshaped our view of Mars' history.

 

-   Europa Clipper Mission: Poised for launch by NASA, the Europa Clipper mission is poised to harness remote sensing instruments to explore Jupiter's moon Europa. By delving into the moon's surface and subsurface, this mission aspires to ascertain its potential habitability.

 

5.  Monitoring Changes Over Time

 

-   Chandra, XMM-Newton, and Suzaku: A collaborative venture involving MKI, UCL, SwRI, and MSFC, these missions observed X-rays emanating from Jupiter and Saturn. This research deepened our understanding of these planets'

auroral regions, magnetotails, and dynamic phenomena, through a synergy of X-ray data and optical observations.

 

6.  Observations Beyond the Solar System

 

-   Exoplanet Characterization: Planetary remote sensing techniques have also been employed to study exoplanets, offering valuable insights into their atmospheres, compositions, and potential habitability.

 

Research Techniques in Planetary Remote Sensing

Several advanced research techniques and instruments are pivotal to the success of planetary remote sensing:

 

1.  Radar Mapping (Microwave Remote Sensing)

 

-  Magellan Venus Radar Mapping: MKI's leadership in this mission led to the creation of the most detailed topographic maps of Venus to date. Radar remote sensing unveiled the intricate terrain of Venus, providing essential data on surface roughness and dielectric properties.

2.  LIDAR (Light Detection and Ranging)

 

-  Mars Global Surveyor LIDAR Experiment: Through a meticulous analysis of LIDAR echoes from CO2 clouds in Mars' polar regions, MKI scientists contributed significantly to understanding the Martian atmosphere. These findings have illuminated the behavior of polar clouds and their interaction with the planet's surface features.

 

 

3.  X-Ray Spectroscopy (X-Ray Remote Sensing)

 

-   Observations of X-Rays from Jupiter and Saturn: MKI, collaborating with other institutions, has conducted pioneering research by observing X-rays emitted by Jupiter and Saturn. Utilizing instruments aboard Earth-orbiting spacecraft such as Chandra, XMM-Newton, and Suzaku, researchers have probed X-ray emissions originating from Jovian auroras, Saturn's magnificent rings, and moons like Io and Europa.

Topographic Mapping of Celestial Bodies

1.    The Moon

The history of lunar topographic mapping stretches back to the early days of space exploration. The first spacecraft image of the Moon was captured by Russia's Luna 3 in 1959. In the 1960s, the U.S. Ranger project launched several spacecraft successfully, leading to lunar maps based on Ranger images.

 

Significant advancements occurred during the Apollo missions, particularly Apollo 15, 16, and 17, which deployed automated mapping, stereo panoramic cameras, and laser altimeters for 3D control point assignment. These missions laid the groundwork for precise lunar topography measurements.

 

The Clementine project, launched in 1994, marked a major milestone in lunar surface mapping. It included various camera systems and a laser altimeter to produce 3D topographic products. The United States Geological Survey (USGS) created lunar mosaic basemaps using data from Clementine, providing global coverage at a 100 m resolution.

In the 21st century, missions like SMART-1, SELENE, Chang'e, and Chandrayaan-1 continued lunar exploration. They carried instruments such as stereo cameras and laser altimeters, offering improved spatial resolution and coverage. The Lunar Reconnaissance Orbiter (LRO), launched shortly after Chandrayaan-1, featured even higher-resolution cameras and produced a global DEM with remarkable precision.

 

Subsequent missions by CNSA (Chang'e series) and ISRO (Chandrayaan-2) expanded our knowledge of lunar topography. To reduce vertical offsets between different lunar DEMs, surface matching technology was employed.

 

Integration of multiple topographic datasets also became common practice. For example, imagery and laser altimeter data from Chang'e-1 were integrated to create updated local DEMs, and similar techniques were applied to improve the performance of lunar DEMs.

 

The Korean Pathfinder Lunar Orbiter (KPLO) entered lunar orbit in 2023, equipped with the ShadowCam to observe permanently shadowed regions (PRRs) for signs of frozen water.

 

 

 

2.    Mars

Mapping the topography of Mars has evolved over centuries. Early efforts by astronomers like Schiaparelli in the 19th century provided orientation and georeferencing for Martian maps. However, it wasn't until the 1960s, with the success of Mariner missions, that actual topographic images of Mars became available.

 

Mariner 9, launched in 1971, was a significant milestone in Martian mapping. It provided data for mapping the entire planet, and this data became the basis for mapping entire planets from space.

 

The Viking 1 and Viking 2 orbiters, launched in 1976, provided a wealth of images with resolutions ranging from 7 m to 1000 m. The Viking Landers also contributed by providing geodetic landmarks on Mars.

 

The Mars Orbiter Laser Altimeter (MOLA) marked a leap forward in Martian topography mapping. It collected laser reflection data and generated a global DEM with impressive accuracy.

 

Later missions like MGS, MOC, MRO, and MARS Express further enhanced Martian mapping. High-resolution stereo cameras and laser altimeters on these spacecraft provided detailed topographic data. The High Resolution Imaging Science Experiment (HiRISE) on MRO, with a resolution of 40 cm GSD, revolutionized planetary surface mapping.

 

The ExoMars Trace Gas Orbiter and the Indian Mars orbiter, Mangalyaan, also contributed to Martian mapping efforts. The Chinese Mars mission, Tianwen-1, completed topographic mapping of a specific landing site.

These missions have allowed the construction of detailed DEMs, benefiting various scientific studies of Martian geology, geomorphology, and more.

 

This new section provides a comprehensive overview of the topographic mapping of the Moon and Mars, highlighting key missions, instruments, and advancements in our understanding of these celestial bodies' surfaces.

3. Trans-Neptunian Object (TNO) Mapping

Mapping the topography of Trans-Neptunian Objects (TNOs), including those in the Kuiper Belt, has been a challenging endeavor. To date, the only successful space mission that has provided topographic information about TNOs is New Horizons.

 

The New Horizons mission achieved remarkable success by mapping Pluto, Charon, and Arrokoth, expanding our understanding of planetary topography into the realm of minor bodies in the outer Solar System. This mission primarily relied on the Long Range Reconnaissance Imager (LORRI) for topographic remote sensing.

 

While the New Horizons mission yielded valuable topographic data and enabled stereo analysis, technical details about the topographic processing of LORRI data, especially concerning geodetic control, remain limited in the published literature.

 

During the mission, approximately 42% of Pluto's surface was mapped using stereo Digital Elevation Models (DEMs) with resolutions ranging from 90 to 1120 meters, along with orthoimage sets covering major surface areas.

Similarly, the Charon mission of New Horizons achieved 40% DEM coverage with resolutions between 0.1 and 1.5 kilometers and orthoimage coverage of the northern hemisphere at a resolution of 300 meters.

Notably, one challenge in the Pluto and Charon missions is the absence of reference height planes or point measurements, as seen in missions to Mars, the Moon, and Venus. Geodetic control for these TNOs primarily relied on navigation data.

 

Given the distant and challenging nature of the Kuiper Belt and TNOs, it's uncertain when another mission to this region may occur in the next decade. As a result, future mapping efforts for Pluto and Charon are likely to rely on re- analyses of existing New Horizons datasets, potentially complemented by data from next-generation space telescopes.

 

Mapping TNOs remains a fascinating area of study, with the potential for new discoveries and insights as technology advances and future missions are considered.

 

Conclusion

Planetary remote sensing, coupled with sophisticated research techniques, has ushered humanity into the forefront of space exploration, unveiling the secrets of celestial bodies within our solar system. From the enigmatic topography of Venus to the ever-changing landscapes of Mars and the captivating auroral displays of Jupiter and Saturn, remote sensing instruments have provided a transformative window into the cosmos. As technology continues to advance and new missions are launched, the horizon of planetary remote sensing promises a boundless journey of discovery, further enriching our understanding of these distant worlds and their pivotal role in unraveling the mysteries of the universe . Bridging the gap in understanding of planetary remote sensing technology is crucial to ensure accurate interpretation and dissemination of these remarkable achievements. This journey invites us all to become explorers of the cosmos, to gaze upon the enigmatic topography of Venus, witness the ever-changing landscapes of Mars, and marvel at the captivating auroral displays of Jupiter and Saturn. As a global community, we collaborate to bridge the gap in understanding this remarkable technology, ensuring its accurate interpretation and dissemination.

 

References

1.    Remote Sensing and Data Analyses on Planetary Topography by Jungrack Kim , Shih-Yuan Lin, and Haifeng Xiao

2.    Greeley, R.; Batson, R.M. Planetary Mapping; Cambridge University Press: Cambridge, UK, 1990.

3.    Carder, R.W. Lunar Mapping on a Scale of 1: 1000000. In The Moon; 1962; pp. 117–129. Available online:https://adsabs.harvard.edu/full/1962IAUS...14..117C (accessed on 28 March 2023).

4.  Ford, P.G.; Pettengill, G.H. Venus topography and kilometer-scale slopes. J. Geophys. Res. Planets 1992.

5.    MIT Kavli Institute for Astrophysics and Space Research website. https://space.mit.edu/research/planetary-remote-sensing/

---Harshit Krishna (MS22)