Researchers Discover Nitrogen in Inner Disk that Formed Earth with Implications to Terraform Mars

February 9, 2021. By Kolemann Lutz

Rice University researchers conducted a study evaluating nitrogen isotope compositions of iron meteorites that fell to Earth to demonstrate that much of the nitrogen on Earth came from the inner Solar system, which completely changes the narrative.

A combination of organic volatile elements, hydrogen, oxygen, nitrogen, and carbon are vital to sustain life as we know it on Earth. As an essential component of DNA and proteins, nitrogen is one of the organic elements to support plant growth.

Understanding the origin of life-essential volatiles such as nitrogen (N) in the Solar System and beyond is critical to evaluate the potential habitability of Mars and other celestial bodies. The 21st century atmosphere of Mars lacks nitrogen, which is a key missing element to terraforming Mars.

In 2019, the research team at Rice University claimed that Earth most likely received the bulk of its carbon, nitrogen and other life-essential volatile elements after the planetary collision and giant impact hypothesis around 4.5 billion years ago that created the Moon. It is believed that large quantities of nitrogen in primordial debris that formed Earth have directly shaped the Earth’s present atmosphere that is 78% nitrogen.

As nitrogen has been seeping out along the molten cracks in the planet's crust since planetary formation, researchers conducted simulations in 2018 to determine the amount of nitrogen in Earth’s outer core to be around 2% by weight at the core-mantle boundary, and about 2.6% by weight at the inner-core boundary.

There has been a prolonged debate lasting many decades over the origin of life-essential volatile elements in Earth and other rocky bodies in the Solar system. Whether the organic elements began during the formation of the inner planets or were delivered from the outer Solar System is not well understood.

Researchers traditionally believed that the inner disk of the Solar system within Jupiter’s orbit was too hot for nitrogen and other organic elements to condense from gases into solids, suggesting the notion that organic volatiles such as nitrogen were delivered from the outer Solar system. However, new evidence indicates that only some of the planet’s nitrogen came from beyond Jupiter.

In a study published in January 2021, Rice University graduate student and lead author Damanveer Grewal, Rice faculty member Rajdeep Dasgupta and geochemist Bernard Marty at the University of Lorraine, France analyzed iron meteorites in tact on Earth’s surface to discover a distinct nitrogen isotope signature in the dust around the inner rocky planets, or protoplanets, that is from within 300,000 years of the formation of Solar system.

Iron(fe) meteorites formed at the same of the present-day rocky planets and can be considered remnants of the cores of the inner planets. Their results indicated all iron meteorites from the outer disk were rich in nitrogen-15 and those from the inner disk contained lower concentrations of the nitrogen-14 isotope.

Thus, the early Solar system was divided into two reservoirs of nitrogen within the first few million years and Earth gathered its nitrogen from both the region beyond Jupiter’s orbit and the dust in the inner disk, settling the prolonged debate about how nitrogen was delivered to the inner planets.

“Our work completely changes the current narrative,” Grewal said. “We show that the volatile elements were present in the inner disk dust, probably in the form of refractory organics, from the very beginning. This means that contrary to current understanding, the seeds of the present-day rocky planets — including Earth — were not volatile-free.”

The finding is significant toward understanding the potential habitability of exoplanets. “At least for our own planet, we now know the entire nitrogen budget does not come only from outer solar system materials,” said Dasgupta, Rice’s Maurice Ewing Professor of Earth, Environmental and Planetary Sciences.

As Mars’ current atmosphere is composed of 2.7% nitrogen, 95% CO2, and 1.9% Argon, researchers assume that there is abundance of nitrogen locked in mineral deposits because nitrogen is one of the most abundant elements in the Solar system and Mars formed from the same protoplanetary disk as Earth.

In July 2015, the SAM instrument on the Mars Curiosity rover analyzed samples of windblown sand and dust to find nitrogen in the form of nitric oxide (NO). This realization has led NASA to believe that nitrates (NO3), the only biologically useful form of nitrogen on Mars, are widespread on Mars with concentrations as high as 1,100 parts per million at drill sites.

After Curiosity identified tridymite in a rock sample from Gale Crater, scientists believe silicic volcanism has been much more common in the planet’s history.

Silicon dioxide (SiO2), also known as silica, is the most abundant rock-forming compound on Earth and Mars, and is the predominant molecular constituent of volcanic rocks and magmatic liquids. These silicate minerals are known to harbor substantial amounts of nitrogen when superheated in lava. Moreover, sinoite (Si2N2O) is relatively abundant in chondrite asteroids, which can hold up to 27.96% nitrogen by weight.

The Noachian period 3.7 billion years ago was a time of intense volcanism with most of it centered in the Tharsis region, or Tharsis bulge. As the Martian crust consists mostly of volcanic basalt rock, volcanic features were prevalent over large portions of the surface throughout the late Amazonian period up until 500 million years ago.

Large silica-rich magma storage regions or nitrite (NO2) and nitrate (NO3) rich locations on Mars could become a greater priority in the selection of candidate landing sites. However, greater spatial resolutions from spectroscopy instrumentation and analysis are needed to observe nitrogen concentrations in candidate landing sites.

As one of the essential building blocks for life, nitrogen is typically converted by cyanobacteria from inert atmospheric nitrogen into organic nitrate (NO3) or ammonia (NH4) in soil, which are essential nutrients to grow crops.

In situ nitrogen extraction and utilization becomes equally as important as water ice mining

to live off the land and establish self-sustaining settlements”, mentioned by Kolemann lutz, Cofounder at MarsU.

Researchers at Mars University are seeking to collaborate to develop the research and scientific literature around nitrogen settlement estimates and requirements as well as developing the technologies and materials involved in nitrogen supply chain and importation.

Some researchers propose that nitrogen could be substituted with other non-toxic inert gases such as argon to increase the atmospheric pressure. Alternatively, because Earth has the most readily available nitrogen in the Solar system, imported nitrogen could become an important component for trade and geoengineering a more habitable biosphere.

Damanveer S. Grewal, Rajdeep Dasgupta & Bernard Marty. A very early origin of isotopically distinct nitrogen in inner Solar System protoplanets. Nature Astronomy Journal. January, 21, 2021.

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