May 10, 2024New Horizons Scientists Make Landmark Ultraviolet Observations of the Heliosphere, Universe and the Local Interstellar Medium

NASA spacecraft’s distant position avoids dust and ultraviolet light pollution closer to the Sun

Scientists with NASA’s New Horizons mission are pursuing new research goals and making unique astrophysical and heliospheric observations with the suite of instruments onboard the New Horizons spacecraft. This unique project takes advantage of the spacecraft’s current position in the distant Kuiper Belt, where observations avoid several kinds of viewing obscurations closer to Earth.

The interplanetary New Horizons was launched in 2006. Its central goal was to gain a greater understanding of the development of Pluto, the Kuiper Belt and the solar system. Its historic flybys of Pluto in 2015 and the Kuiper Belt Object Arrokoth in 2019 generated both worldwide headlines and numerous groundbreaking scientific results, and the spacecraft has since sent back remarkable images and other data from the edge of the solar system.

“A good tool can be used for many things,” said Joel Parker, New Horizons deputy project scientist from the Southwest Research Institute (SwRI) in Boulder, Colorado. “It’s exciting to develop new uses for New Horizons to add to its originally intended uses as the mission continues. The spacecraft and its powerful suite of instruments are in excellent health as the mission continues through the Kuiper Belt. From that perch, New Horizons is in a unique position not only to continue planetary science work, but also to contribute to important studies for astrophysics and heliophysics.”

Parker is a longtime member of the New Horizons team, serving as a member of the science team and the project manager for the spacecraft’s ultraviolet spectrograph, Alice.

“New Horizons is uniquely positioned to make astrophysical observations that are difficult or impossible to make here on Earth or even from orbit,” Parker said. “Many things can obscure observations, but one of the biggest problems is the dust in the inner solar system. It may not be obvious when you look up into a clear night sky, but there is a lot of dust in the inner part of the solar system. There is also a great deal of obscuration at certain ultraviolet wavelengths at closer distances due to the hydrogen that pervades our planetary system, but which is much reduced out in the Kuiper Belt and the outer heliosphere.”

The dust is the result of asteroids, comets and other objects colliding or shedding dust for other reasons. As New Horizons has traveled farther away from Earth to the Kuiper Belt and beyond, the dust becomes considerably less dense. Additionally, contamination from the Sun and its light scattering off dust and hydrogen gas is diminished near the spacecraft’s position at the edge of the solar system.

“It’s like driving through a thick fog, and when you go over a hill, it’s clear,” Parker said. “Suddenly, you can see things that were obscured. When you’re trying to look for a very faint light far outside our solar system or beyond our galaxy, that obscuration creates a challenge.”

Earth-based observations of objects beyond the solar system must account for the interference of dust and light, requiring scientists to make models estimating how significantly their view is obstructed. The New Horizons team takes advantage of the spacecraft’s position in the Kuiper Belt to gain a better understanding of these models’ accuracy, and to make observations without having to make corrections based on dust models.

“If we measure how the ‘fog’ changes as we move farther out, we can make better models for our observations from Earth,” Parker said. “With more accurate models, we can more easily subtract the effects of light and dust contamination.”

The New Horizons team is particularly interested in the cosmic optical background and what it reveals about the evolution of galaxies over the history of the universe, including clues about the nature of dark matter. Team members are also interested in observing the cosmic ultraviolet background, which could shed light on star formation rates, interstellar shocks and dust scattering, as well as improving existing observation models and mapping the hydrogen distribution in the outer heliosphere and nearby parts of the interstellar medium.

“The landmark planetary science New Horizons is doing and continues to do are amazing, but it’s also amazing to see the spacecraft contributing significantly to other important fields of science, such as astrophysics and heliophysics,” said Alan Stern, the New Horizons principal investigator from SwRI.

SwRI directs the mission via Principal Investigator Alan Stern and leads the science team, payload operations and encounter science planning. The Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, designed, built and operates the New Horizons spacecraft, and manages the mission for NASA’s Science Mission Directorate. The MSFC Planetary Management Office provides the NASA oversight for the New Horizons mission. New Horizons is part of the New Frontiers Program managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.

The red line marks the path of the New Horizons spacecraft into the distant Kuiper Belt. The spacecraft’s current position in the Kuiper Belt, where observations can avoid interference closer to Earth, allows it to make unique astrophysical observations without the light and dust pollution in the inner solar system. (Credit: NASA/Johns Hopkins APL/SwRI)

New Horizons mission scientists and external colleagues are taking advantage of the New Horizons spacecraft’s position in the distant Kuiper Belt to make unique astrophysical and heliospheric observations. Alice, the ultraviolet spectrograph on the spacecraft, performed 75 great circle scans of the sky in September 2023, for a total of 150 hours of observations. These data focus on the light from hydrogen atoms in the ultraviolet Lyman-alpha wavelength across the sky as seen from New Horizons' vantage point in the distant solar system. This map shows the data from the scans overlaid on a smoothed model of the expected Lyman-alpha background. (Credit: NASA/Johns Hopkins APL/SwRI)