Background
The second NASA New Horizons (NH) extended mission (KEM-2) uses the NH spacecraft for three scientific disciplines: planetary science, heliophysics, and astrophysics. The astrophysics observations include Cosmic Optical Background (COB) Mapping, Cosmic UV Background (CUVB) mapping, and Local Interstellar Medium (LISM) UV mapping.
Approach
This Presidential Discretion Internal Research (PDIR) project is to reduce and analyze the astrophysical KEM-2 data acquired by the SwRI-built Alice instrument on NH for the latter two of the above categories (i.e., LISM and CUVB mapping) and publish the results in referred journals. This work is to establish the SwRI team in this field and position us for future funding opportunities.
Accomplishments
We are happy to report that this project was successful in producing two papers and several SwRI staff have broadened their skillset in analysis of astrophysical UV data.
One of the papers, already published, provided an unprecedented all-sky Lyman-alpha ultraviolet map of the sky. The other paper was originally envisioned to analyze the Cosmic Ultraviolet Background but was refocused to utilize the high-resolution Alice ultraviolet scans that our team is uniquely able to analyze.
LISM mapping. The data were retrieved and reduced, and many Lyman-alpha (Lyα) maps were made and compared with known LISM structures. This is the first detailed all-sky map of Lyα emission observed from the outer solar system, where the Galactic and solar contributions to the observed brightness are comparable, and the solar contribution can be reasonably removed. Our results show that the overall average brightness level of the Lyα emission can be explained as largely due to early-type stars and hot gas shining on and ionizing the hydrogen of the interior walls of the Local Hot Bubble surrounding the Sun.
High Resolution Scans. These data were a pair of orthogonal scans covering a 4º×4º region of the sky near the galactic south pole. We found that the brightness of the UV background remains relatively constant over that region, except for areas near a few bright stars. We detect a Lyα enhancement near the location of a fast-moving hot sub dwarf that could result from H-emissions from a bow shock. We do not find correlations with dust structures seen observations by Planck space telescope. Our analysis confirms the results of the LISM mapping at lower spatial resolutions. The near-constant Lyα brightness supports the interpretation that scattering of hydrogen within our local bubble produces a nearly uniform Lyα distribution.
Publications
Gladstone, G. R., Shull, J. M., Pryor, W. R., Slavin, J., Kammer, J. A., Becker, T. M.,
Lauer, T. R., Postman, M., Spencer, J. R., Parker, J. Wm., Retherford, K. D., Velez, M. A., Versteeg M. H., Davis, M. W., Froning, C. S., Ertley, C. D., Cunningham, N., Murthy, J., Henry, R. C., Redfield, S., Lisse, C. M., Singer, K. N., Verbiscer, A. J., Brandt, P. C., Stern, S. A. (2025), “The Lyα sky as observed by New Horizons at 57 AU.” The Astronomical Journal, 169, 27
Becker, T. M., Gladstone, G. R., Parker, J. Wm., Shull, J. M., Reutschle, S., Redfield, S., Kammer, J. A., Cunningham, N., Postman, M., Murthy, J., Froning, C. S., Stern, S. A. (2025), “Interstellar ultraviolet Ly-α measurements from the New Horizons P-Alice instrument.” The Astronomical Journal, in prep.
Presentations
Gladstone, R., Shull, M., Pryor, W., Slavin, J., Kammer, J., Becker, T., Lauer, T., Postman, M., Parker, J., Spencer, J., Velez, M., Retherford, K., Versteeg, M., Davis, M., Froning, C., Ertley, C., Cunningham, N., Redfield, S., Murthy, J., Henry, R., Lisse, C., Singer, K., Verbiscer, A., Brandt, P., Stern, A., and New Horizons Science Team (2025), “New Horizons UV Observations of Lyman alpha in the Local Interstellar Medium.” American Astronomical Society Meeting #245, January 2025.