Parker Solar Probe Encounters


Parker Solar Probe science is conducted in a series of “encounters” centered around each perihelion, as well as during multiple flybys of Venus. The table below provides the times and distances of each perihelion, and information about each encounter and Venus flyby are given in sections below. For information on coordinating with PSP for an encounter, please contact Robert C. Allen (



Time (UT)

Distance from Center of Sun

Venus Flyby 1

Closest Approach: 2018-10-03/08:44

0.7 au

Encounter 1

Perihelion: 2018-11-06/03:27

0.17 au (35.6 RS)

Encounter 2

Perihelion: 2019-04-04/22:39

0.17 au (35.6 RS)

Encounter 3

Perihelion: 2019-09-01/17:50

0.17 au (35.6 RS)

Venus Flyby 2

Closest Approach: 2019-12-26/18:14

0.7 au

Encounter 4

Perihelion: 2020-01-29/09:37

0.13 au (27.8 RS)

Encounter 5

Perihelion: 2020-06-07/08:23

0.13 au (27.8 RS)


Venus Flyby 1


On the way into the first encounter, Parker Solar Probe conducted a Venus Flyby, in which measurements were taken of the Venusian bowshock. These flybys provide much needed information into the near-Venus space environment and allow for exciting research outside of the primary mission of Parker Solar Probe.


Encounter 1


The first perihelion of Parker Solar Probe reached a solar distance of 0.17 au (35.6 RS), breaking the record as the closest human-made object to the Sun. Findings from the first two encounters were reported in four Nature articles (1, 2, 3, 4) and as a set of over 50 articles in a special issue of The Astrophysical Journal Supplement series (ApJS).


See also ENLIL predictions from Helioweather for Encounter 1.

PSP Orbit for Encounter 1


Encounter 2


The second Parker Solar Probe encounter also reached a solar distance of 0.17 au (35.6 RS) and provided additional insight into the structure of the solar wind in the inner heliosphere. Findings from the first two encounters were reported in four Nature articles (1, 2, 3, 4) and as a set of over 50 articles in a special issue of ApJS.


See ENLIL predictions from Helioweather for Encounter 2.

PSP Encounter Orbit 2


Encounter 3

The third encounter of Parker Solar Probe provided an additional snapshot of the inner heliosphere down to 0.17 au (35.6 RS), complementing those from the first two encounters.


See ENLIL predictions from Helioweather for Encounter 3.

PSP Encounter Orbit 3


Venus Flyby 2


The second Venus flyby allowed for additional measurements of the bowshock of Venus, and allowed Parker Solar Probe to lower its perihelion to 27.8 RS for Encounter 4.


Encounter 4


The orbit of Parker Solar Probe (PSP) during the 4th encounter with the Sun presented a unique opportunity for a multi-mission and multi-observatory collaboration as the 4th perihelion occurred nearly at the Sun-Earth line. This unprecedented configuration allowed ground-based solar observatories to measure the solar surface that PSP was magnetically connected to while PSP simultaneously measured the near-Sun environment at the closest distance to the Sun recorded to date (27.8 RS). Additionally, near-Earth missions (e.g., ACE, ARTEMIS, and MMS) could then measure this solar wind once it reached 1 au to study the evolution of solar wind structures as they propagate radially outward from the Sun. Probes within the magnetosphere of Earth, and observatories focused on the ionosphere, could then study how these structures affect the near-Earth environment. To take advantage of this great opportunity for large-scale coordinated science, the PSP Project Science team and the Whole Heliosphere and Planetary Interactions (WHPI) group organized a campaign that has brought together observatories and missions from across the world. This page is meant to contain information and links relevant to the Parker Solar Probe Encounter 4 campaign. For more information, please contact Robert C. Allen (, the PSP Project Science team coordinator for this effort.


Contributing Missions and Observatories


In all, 50 missions and observatories took part in this campaign. The table below provides information on the number of missions/observatories by type. A full list of missions and observatories involved can be found here.

Observatory/mission type

Number contributing to encounter 4

Ground-based optical observatories


Ground-based radio observatories


Space-based missions


Ground-based geospace observatories



Footpoint Predictions


To facilitate targeted measurements from the solar observatories, predictions of the PSP footpoints were generated daily and provided via the WHPI website by the PSP modeling team (leads: Pete Riley and Sam Badman). Consensus predictions were generated using several PFSS models and MHD simulations.

Heliographic Carrington footpoints of PSP

Heliographic Carrington footpoints of PSP on the day of Perihelion 4: one footpoint per day plotted in Carrington coordinates (latitude-longitude) and with error bars in latitude and longitude for ensemble predictions. Also shown in this plot is the most recent GONG-ADAPT current sheet generated by the UCB model (red), and the date-stamped PSP trajectory in Carrington coordinates (grey) (Courtesy of Sam Badman; SDO/AIA 193A synoptic map produced by David Stansby).

Helioprojective PSP predicted footpoints on the day of Perihelion 4: one footpoint per day plotted on the solar disk. Colored dots show predictions from a range of models (Courtesy of Sam Badman).

Conjunction with In Situ Observations


In addition to magnetic footpoint mapping for solar observers, ballistic mappings were performed to estimate when solar wind observed at PSP may reach 1 au at either STEREO-A or near-Earth observers. This shows that the footpoints of STEREO-A and PSP may have been near each other from Jan 26th, 2020 to Jan 28th, 2020 (where the red lines cross the black horizontal line at 0), while the footpoints of Earth and PSP may have been close from Jan 29th, 2020 until Jan 31st, 2020 (where the blue lines cross the zero-line).

Difference in the Carrington longitude


Difference in the Carrington longitude of footpoints between PSP and Earth (blue) and between PSP and STEREO-A (red) for different solar wind velocities from a ballistic propagation (Courtesy of Sam Badman).


Movie showing the footpoint locations from ballistic mapping of PSP (yellow), STEREO-A (red), and Earth (blue) for 300 and 600 km/s solar wind during encounter 4 (Courtesy of Sam Badman; SDO/AIA 193A synoptic map produced by David Stansby).

Encounter 4 Coordination Planning Presentations


Ongoing Efforts


Sessions have been proposed related to Encounter 4 activities and subsequent observations for the upcoming 2020 SHINE meeting and the joint GEM/SHINE day this summer. Additionally, this encounter will be discussed at the upcoming WHPI workshop on September 14 – 18, 2020.


Links to Websites Related to Encounter 4


See the WHPI website for Encounter 4

See ENLIL predictions from Helioweather for Encounter 4



Encounter 5



The fifth encounter of Parker Solar Probe provides measurements of the inner heliosphere down to 0.13 au (27.8 RS), the same distance as Encounter 4. The orbit configuration of PSP and Earth will allow for footpoint observations at the limb starting near the time of the PSP perihelion.


PSP Encounter Orbit 5


Ballistic Propagation


Ballistic propagation predictions, provided by Sam Badman, give an early prediction of when the PSP footpoint may cross into view from Earth. Below is a movie showing the (left) helioprojective viewpoint and (right) Carrington coordinates of PSP during encounter 5. The orange dashed line represents the limb from the point of view of Earth. Ballistic footpoints for solar wind speeds of 200 (blue), 400 (orange), and 600 (red) km/s speeds are shown in both plots (unless they are not visible from Earth in the left panel). The Carrington meridian is shown with the blue curve in the left panel and is dashed when on the opposite side of the Sun as Earth. These estimates predict that the ballistic footpoint of PSP will cross over the East limb on June 7th (0600 UTC for 200 km/s, 1200 UTC for 400 km/s, and 1800 UTC for 600 km/s). This is remarkably close to the perihelion (June 7th, 0800 UTC).

Using data from the movie above, the panels in the image below show the course of predicted PSP footpoint locations during Encounter 5. The blue circles in the left panel mark, with the dates labeled, when the PSP footpoints are in view of the Earth for a solar wind speed of 400 km/s. This is shown in the helioprojective frame. The predicted footpoints in the right panel are shown in Carrington coordinates over the full encounter. For this solar wind speed, these ballistic estimates predict that the PSP footpoints will be visible from the Earth by June 8th.


PSP Orbit for Encounter 5


Consensus footpoint predictions


The PSP modeling team are supporting this encounter by providing consensus footpoint predictions during the second half of the encounter. These predictions will be updated here weekly during the encounter starting on June 5th.









Page Last Modified: June 5, 2020