Gateway into Inner Solar System Discovered, Finding May Alter Fundamental Understanding of Comet Evolution

A new study may fundamentally alter our understanding of how comets arrive from the outskirts of the solar system and are funneled to the inner solar system coming closer to Earth. 

At the EPSC-DPS Joint Meeting 2019 in Geneva, planetary scientist Dr. Jordan Steckloff presented the discovery of an orbital ‘Gateway’ through which many comets pass just before they approach our Sun. The Gateway was uncovered as part of a suite of orbital simulations of Centaurs, a group of small icy bodies traveling on chaotic orbits between Jupiter and Neptune. The study team modeled the evolution of bodies from beyond Neptune’s orbit, through the giant planet region and inside Jupiter’s orbit. These icy bodies are considered nearly pristine remnants of material from the birth of our solar system.

For a long time, evolution pathwayof comets from their original formation location inwards towards the Sun, has been debated. “How do new comets, controlled by Jupiter’s influence, replace those that are lost? Where is the transition between residing in the outer solar system, as small dormant bodies, and becoming active inner solar system bodies, exhibiting a widespread gas and dust coma and tail?” asked Steckloff. These questions remained a mystery until now. “What we discovered, the Gateway model as a ‘cradle of comets’, will change the way we think about the history of icy bodies,” said Dr. Gal Sarid (University of Central Florida), the lead scientist for the study. 

Centaurs are thought to originate in the Kuiper Belt region beyond Neptune and are considered as the source population of Jupiter Family Comets (JFCs), which occupy the inner solar system. The chaotic nature of Centaur orbits obscures their exact pathways making it difficult to predict their future as comets.  When icy bodies like Centaurs or comets approach the Sun, they begin to release gas and dust to produce the coma and extended tails that we refer to as comets. This display is among the most impressive phenomena observable in the night sky, but it is also a fleeting flicker of beauty that is rapidly followed by either the destruction of the comet or its evolution to a dormant state, said team member Dr. Kathryn Volk (Lunar and Planetary Laboratory, The University of Arizona). 

The original goal of the investigation was to explore the history of a peculiar Centaur object – 29P/Schwassmann-Wachmann 1 (SW1). It is a mid-sized Centaur in a nearly circular orbit just beyond Jupiter. SW1 has long puzzled astronomers with its high activity and frequent explosive outbursts that occur at a distance from the Sun where ice should not effectively vaporize. Both its orbit and activity put SW1 in an evolutionary middle ground between the other Centaurs and the JFCs. The research team wanted to explore whether SW1’s current circumstances were consistent with the orbital progression of the other Centaurs. 

“More than one in five Centaurs that we tracked were found to enter an orbit similar to that of SW1 at some point in their lifetime,” said Dr. Maria Womack (Florida Space Institute), scientist and co-author of the study. “Rather than being a peculiar outlier, SW1 is a Centaur caught in the act of dynamically evolving into a JFC.” 

In addition to the commonplace nature of SW1’s orbit, the simulations lead to an even more surprising discovery. “Centaurs passing through this region are the source of more than two thirds of all JFCs, making this the primary Gateway through which these comets are produced,” said team member Dr. Walter Harris (Lunar and Planetary Laboratory, The University of Arizona). The Gateway region does not hold resident objects for long, with most Centaurs becoming JFCs within a few thousand years. This is a short portion of any solar system object’s lifetime, which can span millions and sometimes billions of years. 

The presence of the Gateway provides a long sought after means of identifying the Centaurs on an imminent trajectory toward the inner solar system. SW1 is currently the largest and most active of the handful of objects discovered in this Gateway region, which makes it a “prime candidate to advance our knowledge of the orbital and physical transitions that shape the comet population we see today,” said team member Dr. Laura Woodney (California State University San Bernardino).

Our understanding of comets is intimately linked to knowing our solar system’s early composition and the evolution of conditions for atmospheres and life to arise, the researchers said. The results of this study have recently been accepted for publication in The Astrophysical Journal Letters.  

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The authors of this study are all members of the Chimera mission concept, a proposed mission to send a spacecraft to orbit 29P/Schwassmann-Wachmann 1 for a 30 month investigation of its evolution, dynamics and activity. This work is funded in part by grants from NSF (1615917, 1824869, 1910275, and 1945950) and NASA (80NSSC18K0497, NNX15AH59G, 80NSSC19K0785).

Anita Heward
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Notes for Editors

EPSC-DPS Joint Meeting 2019
The 2019 Joint Meeting (www.epsc-dps2019.eu) of the European Planetary Science Congress (EPSC) of the Europlanet Society and the Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS) will take place at the Centre International de Conférences de Genève (CICG), Geneva, Switzerland, from Sunday 15 to Friday 20 September 2019. More than 1950 abstracts have been submitted and over 1500 planetary scientists from Europe, the US and around the world are expected to attend the meeting, making it one of the largest gatherings of planetary scientists held in Europe to date.
The EPSC-DPS Joint Meeting 2019 will be the third time that EPSC and the DPS Annual Meeting have been held together.
Follow: @europlanetmedia #EPSCDPS2019

Europlanet
The Europlanet Society, launched in September 2018, is an organization for individual and corporate members to promote the advancement of planetary science and related fields in Europe. The Society provides Europe’s planetary science community with a platform to exchange ideas and personnel, share research tools, data and facilities, define key science goals for the future, and engage stakeholders, policy makers and European citizens with planetary science. The Europlanet Society is the parent organisation of the European Planetary Science Congress (EPSC).
Europlanet Society website: www.europlanet-society.org
EPSC-DPSC 2019 Joint Meeting 2019 website: www.epsc-dps2019.eu

DPS
The Division for Planetary Sciences (DPS), founded in 1968, is the largest special-interest Division of the American Astronomical Society (AAS). Members of the DPS study the bodies of our own solar system, from planets and moons to comets and asteroids, and all other solar-system objects and processes. With the discovery that planets exist around other stars, the DPS has expanded its scope to include the study of extrasolar planetary systems as well.

The AAS, established in 1899, is the major organization of professional astronomers in North America. The membership (approx. 7,500) also includes physicists, mathematicians, geologists, engineers, and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy. The mission of the AAS is to enhance and share humanity’s scientific understanding of the universe, which it achieves through publishing, meeting organization, education and outreach, and training and professional development.