A spacecraft has 'touched' the sun for the first time

Date:
December 14, 2021
Source:
American Physical Society
Summary:
On April 28, 2021, NASA's Parker Solar Probe reached the sun's
extended solar atmosphere, known as the corona, and spent five hours
there. The spacecraft is the first to enter the outer boundaries
of our sun.



FULL STORY ========================================================================== [Illustration of sun | Credit: (c) Kittiphat / stock.adobe.com]
Illustration of sun (stock image).

Credit: (c) Kittiphat / stock.adobe.com [Illustration of sun | Credit:
(c) Kittiphat / stock.adobe.com] Illustration of sun (stock image).

Credit: (c) Kittiphat / stock.adobe.com Close NASA's Parker Solar Probe
reached the sun's extended solar atmosphere, known as the corona, and
spent five hours there. The spacecraft is the first to enter the outer boundaries of our sun.


========================================================================== "This marks the achievement of the primary objective of the Parker
mission and a new era for understanding the physics of the corona,"
said Justin C. Kasper, the first author, Deputy Chief Technology Officer
at BWX Technologies, and a professor at the University of Michigan. The
mission is led by the Johns Hopkins University Applied Physics Laboratory (JHU/APL).

The probe made the first direct observations of what lies within the
sun's atmosphere, measuring phenomena previously only estimated.

The sun's outer edge begins at the Alfve'n critical surface: the point
below which the sun and its gravitational and magnetic forces directly
control the solar wind. Many scientists think that sudden reverses in
the sun's magnetic field, called switchbacks, emerge from this area.

"The concept of sending spacecraft into the magnetized atmosphere of the
sun - - sufficiently close that the magnetic energy is greater than both
ion and electron kinetic and thermal energy -- predated NASA itself,"
said Kasper.

In 2018, NASA launched Parker Solar Probe with the goal of finally
reaching the sun's corona and making humanity's first visit to a star.



==========================================================================
This past April, the probe spent five hours below the Alfve'n critical
surface in direct contact with the sun's plasma. Below that surface,
the pressure and energy of the sun's magnetic field was stronger than
the pressure and energy of the particles. The spacecraft passed above
and below the surface three separate times during its encounter. This
is the first time a spacecraft has entered the solar corona and touched
the atmosphere of the sun.

Surprisingly, the researchers discovered that the Alfve'n critical surface
is wrinkled. The data suggest that the largest and most distant wrinkle of
the surface was produced by a pseudostreamer -- a large magnetic structure
more than 40 degrees across, found back on the innermost visible face
of the sun. It is not currently known why a pseudostreamer would push
the Alfve'n critical surface away from the sun.

Researchers noticed far fewer switchbacks below the Alfve'n critical
surface than above it. The finding could mean that switchbacks do not
form within the corona. Alternatively, low rates of magnetic reconnection
on the sun's surface could have pumped less mass into the observed wind
stream, resulting in fewer switchbacks.

The probe also recorded some evidence of a potential power boost just
inside the corona, which may point to unknown physics affecting heating
and dissipation.

"We have been observing the sun and its corona for decades, and we know
there is interesting physics going on there to heat and accelerate the
solar wind plasma. Still, we cannot tell precisely what that physics is,"
said Nour E.

Raouafi, the Parker Solar Probe Project Scientist at JHU/APL. "With
Parker Solar Probe now flying into the magnetically-dominated corona,
we will get the long-awaited insights into the inner workings of this mysterious region." The observations took place during Parker Solar
Probe's eighth encounter with the sun. All data is publicly available
in the NASA PSP archive. Several previous studies predicted the probe
would first pass within the sun's boundaries in 2021.



==========================================================================
The fastest known object built by humans, Parker Solar Probe has made
many new discoveries since its launch, including on explosions that
create space weather and the dangers of super-speedy dust.

The new findings suggest that direct observations by spacecraft have
much to illuminate about the physics of coronal heating and solar wind formation.

Having achieved its goal of touching the sun, Parker Solar Probe will
now descend even deeper into the sun's atmosphere and linger for longer
periods of time.

According to Gary Zank, a coinvestigator on the probe's Solar Wind
Electrons Alphas and Protons (SWEAP) instrument and a member of the
National Academy of Sciences, "It is hard to overstate the significance of
both the event and the observations made by Parker Solar Probe. For over
50 years, since the dawn of the space age, the heliospheric community
has grappled with the unanswered problem of how the solar corona is
heated to well over a million degrees to drive the solar wind. The first measurements of the sub-Alfve'nic solar wind may represent the most major
step forward in understanding the physics behind the acceleration of the
solar wind since the formative model by Parker." "This event is what many heliophysicists have dreamed about for most of their careers!" Zank added.

The results, published in Physical Review Letters, were announced in a
press conference at the American Geophysical Union Fall Meeting 2021 on December 14.

========================================================================== Story Source: Materials provided by American_Physical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. J. C. Kasper, K. G. Klein, E. Lichko, Jia Huang,
C. H. K. Chen, S. T. Badman, J. Bonnell,
P. L. Whittlesey, R. Livi, D. Larson, M. Pulupa, A. Rahmati,
D.

Stansby, K. E. Korreck, M. Stevens, A. W. Case,
S. D. Bale, M. Maksimovic, M. Moncuquet, K. Goetz,
J. S.

Halekas, D. Malaspina, Nour E. Raouafi, A. Szabo, R. MacDowall,
Marco Velli, Thierry Dudok de Wit, G. P. Zank. Parker Solar
Probe Enters the Magnetically Dominated Solar Corona. Physical
Review Letters, 2021; 127 (25) DOI: 10.1103/PhysRevLett.127.255101 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211214134947.htm

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