Io Science in GEM

The Galileo Europa Mission (GEM) began in December 1997 as NASA's Galileo spacecraft successfully completed its nominal mission (11 orbits of Jupiter). With new insights into the Jovian system, more intriguing puzzles, and a healthy spacecraft already in orbit around Jupiter, GEM was proposed and approved for orbits 12 through 25. This page summarizes the scientific goals for and observations of Jupiter's moon, Io, which are planned during GEM.

Galileo SSI Observations of Io

Eclipse observations in orbits 12, 14, 15, and 22.: Eclipse images reveal high-temperature hot spots due to volcanic activity and diffuse glows associated with volcanic plumes and Io's atmosphere.
Six-color coverage at 3.0 km/pixel in orbit 14.: These images will provide the highest resolution six-color coverage of Io's anti-Jovian hemisphere. They will be used to search for iron-rich silicates. These images will also aid in selecting targets for the very high resolution images planned during the close flybys of orbits 24 and 25.
Context frame in orbit 14 for higher resolution images:: A single 2.6 km/pixel frame (with a subsolar position identical to that during the orbit 24 closest approach) will be used to determine the precise location of the higher resolution near-terminator images from orbit 24.
Global low-phase (4°) coverage in four colors in orbits 15, 18, and 21.: These images will be compared to other low-phase images (Voyager, HST, Galileo, and future datasets) to detect surface changes. They will also be compared to high-phase images to determine surface properties. The orbit 15 color set has been expanded to six colors to search for silicates at locations including Pillan, Pele, Babbar, and Isum. The orbit 21 images will be the highest resolution global color images of Io taken by Galileo.
High-phase (75°) coverage in orbit 15.: This will complete global coverage at 70-90° phase in 3 colors.
Moderate-resolution color/albedo mapping in orbit 21.: These images will be the highest resolution coverage from 46° to 210° longitude and will complete the Voyager/Galileo global map at a resolution of 2 km/pixel or better.
Stereo Mapping in orbits 21 and 24.: Nearly the entire anti-Jovian hemisphere of Io will be imaged at 1.4 km/ pixel and at the same phase angle for topographic mapping. The smallest discernable height variations will be about 1/4 km, good enough to map surface variations due to large-scale basins and swells on Io.
Plume inventory in orbits 21 and 22.: This nearly global inventory of active plumes consists of 28 sets of images at 4 to 16 km/pixel resolutions.
High-resolution (100-1000 m/pixel) images in orbits 24 and 25.: About 70 frames in orbit 24, and another 50 in orbit 25 will cover the area from 70° to 230° longitude. These images should include 3 color coverage over especially interesting areas such as Prometheus and Culann. Regions near the terminator, under lighting ideal for viewing the topography of the terrain, could be observed. The plumes of Pele and Pillan (if active) could be observed at about 1 km/pixel on the bright limb.
Very high-resolution (10-100 m/pixel) images in orbits 24 and 25.: About 60 clear frames in orbit 24, and another 40 in orbit 25 will be combined into mosaics of specific features. Potential targets in orbit 24 include Pillan, Marduk, Dorian Montes, Zamama, and Prometheus and could include some high-resolution stereo. If part of Marduk is selected, variations in height of about 5 meters would be discernable and would allow modelling of some of the behaviors of lava on Io. In orbit 25, a pass under the south pole will present several targets, including 26 m/pixel images of the Prometheus eruption column on the bright limb. NIMS (Near Infrared Mapping Spectrometer) and PPR (Photopolarimeter-Radiometer) will obtain concurrent observations of these targets.

Io GEM timeline

All times are the times of the events on the spacecraft in PST (PST = UTC - 8 hours).

EVENT DATE TIME (PST/SCET)

Orbit 12

Start Encounter 15 Dec 1997 00:00

Io eclipse (SSI) 07:42

Io monitoring (NIMS/UVS) 16 Dec 1997 06:10

Io Closest Approach (range = 485,000 km) 11:00

Start Cruise 17 Dec 1997 04:00

Io Science objectives: Io eclipse

Orbit 13

Ganymede Closest Approach (range = 629,900 km) 09 Feb 1998 21:07

Io Closest Approach (range = 438,000 km) 11 Feb 1998 01:37

Callisto Closest Approach (range = 2,260,000 km) 12:28

Io Science objectives: no entry

Orbit 14

Start Encounter 28 Mar 1998 05:00

Io south pole 16:26

Io Closest Approach (range = 252,000 km) 20:48

Io eclipse (SSI) 29 Mar 1998 18:22

Io torus (EUV) 30 Mar 1998 04:00

Start Cruise 17:42

Io Science objectives: full disk, n. and s. pole, eclipse, torus

Orbit 15

Start Encounter 30 May 1998 14:00

Io monitoring (NIMS/UVS) 31 May 1998 06:15

Io Closest Approach (range = 312,000) 14:00

Io eclipse (SSI) 01 Jun 1998 12:39

Io Kanehikili plume (SSI) 14:15

Io torus 19:44

Start Cruise 02 Jun 1998 11:00

Io Science objectives: surface monitoring, Kanehekili plume, high-solar phase map, eclipse, torus, surface composition, tenuous atmosphere

Orbit 16

Io Closest Approach (range = 702,000 km) 19 Jul 1998 21:55

Start Encounter 22:00

Io monitoring (PPR) 20 Jul 1998 04:30

Io torus (UVS) 21 Jul 1998 20:59

Start Cruise 14:47

Io Science objectives: monitoring, torus

Orbit 17

Start Encounter 24 Sep 1998 21:00

Io Closest Approach (range = 800,000 km) 25 Sep 1998 03:09

Io torus (UVS/EUV) 27 Sep 1998 10:55

Start Cruise 28 Sep 1998 01:30

Io Science objectives: Torus

Orbit 18

Start Encounter 21 Nov 1998 04:00

Io polarimetry (PPR) 04:49

Io surface monitoring (SSI) 23:41

Io Closest Approach (range = 996,000 km) 23 Nov 1998 03:11

Io torus (UVS/EUV) 08:29

Start Cruise 11:36

Io Science objectives: surface monitoring, polarimetry, torus

Orbit 19

Start Encounter 30 Jan 1999 18:00

Spacecraft turn for science 31 Jan 1999 09:22

Spacecraft turn for science 20:43

Io polarimetry (PPR) 01 Feb 1999 00:36

Spacecraft turn to Earth-point 04:02

Io Closest Approach (range = 856,000 km) 20:24

Start Cruise 03 Feb 1999 04:16

Io Science objectives: no entry

Orbit 20

Start Encounter 02 May 1999 10:00

Io monitoring (NIMS/UVS) 12:48

Io Closest Approach (range = 789,000 km) 12:49

Start Perijove recording (F&P) 03 May 1999 09:10

Jupiter Closest Approach (range = 669,000 km) 10:11

Io torus (EUV) 04 May 1999 09:39

Start Cruise 13:33

Io Science objectives: monitoring, composition

Orbit 21

Start Encounter 29 Jun 1999 00:00

Io Surface (UVS) 07:01

Io high resolution (SSI) 01 Jul 1999 21:04

Io global (PPR) 21:12

Io Closest Approach (range = 127,000 km) 22:08

Io spectral map (NIMS/UVS) 23:49

Io stereo w/ 124 (SSI) 02 Jul 1999 00:54

Io plume inventory (SSI) 03:58

Io torus 03 Jul 1999 03:00

Start Cruise 06:07

Io Science objectives: global composition, thermal and visual maps, plume inventory

Orbit 22

Start Encounter 11 Aug 1999 04:00

Io Closest Approach (range = 737,000 km) 07:39

Io plume inventory (SSI) 12 Aug 1999 03:59

Chorus waves (PWS) 11:00

Io torus (UVS/EUV) 13 Aug 1999 11:49

Start Cruise 14 Aug 1999 04:23

Io Science objectives: plume inventory

Orbit 23

Start Encounter 13 Sep 1999 13:00

Chorus waves (PWS) 14 Sep 1999 05:00

Start Perijove recording (F&P) 08:30

Io Closest Approach (range = 448,000 km) 14:57

Io torus (UVS/EUV) 15 Sep 1999 21:37

Start Cruise 17 Sep 1999 08:00

Io Science objectives: torus

Orbit 24 -- Details not yet worked out

Start Encounter 09 Oct 1999 20:00

Callisto Closest Approach (range = 1,220,000 km) 10 Oct 1999 01:14

Ganymede Closest Approach (range = 924,000 km) 05:06

Europa Closest Approach (range = 224,000 km) 13:44

Jupiter Closest Approach (range = 396,000 km) 19:04

Io Closest Approach (range = 2,230 km) 21:36

Start Cruise 11 Oct 1999 20:00

Io Science objectives:
Features: Reiden Patera, Zammana, Hi'iaka, Gish bar, Skythia Mons, Amirani, Poliahu, Bosphorus
Stereo coverage: Marduk, Dorian Mons, Prometheus, global
Plumes: Pillian, Pele
Plus magnetosphere

Orbit 25 -- Details not yet worked out

Callisto Closest Approach (range = 1,220,000 km) 24 Nov 1999 15:54

Start Encounter 20:00

Europa Closest Approach (range = 11,500 km) 25 Nov 1999 08:27

Jupiter Closest Approach (range = 407,000 km) 18:08

Io Closest Approach (range = 2,120 km) 20:00

Ganymede Closest Approach (range = 611,,000 km) 23:09

Start Cruise 26 Nov 1999 20:00

Io Science objectives: South pole passage
Features: Prometheus plume, Malik Patera, Tupan Patera, Shamushu Patera, Zal Patera, Culann
Terrains: Plateaus, giant calderas, mountains

EVENT	DATE	TIME (PST/SCET)
Orbit 12
Start Encounter	15 Dec 1997	00:00
Io eclipse (SSI)		07:42
Io monitoring (NIMS/UVS)	16 Dec 1997	06:10
Io Closest Approach (range = 485,000 km)		11:00
Start Cruise	17 Dec 1997	04:00
Io Science objectives: Io eclipse
Orbit 13
Ganymede Closest Approach (range = 629,900 km)	09 Feb 1998	21:07
Io Closest Approach (range = 438,000 km)	11 Feb 1998	01:37
Callisto Closest Approach (range = 2,260,000 km)		12:28
Io Science objectives: no entry
Orbit 14
Start Encounter	28 Mar 1998	05:00
Io south pole		16:26
Io Closest Approach (range = 252,000 km)		20:48
Io eclipse (SSI)	29 Mar 1998	18:22
Io torus (EUV)	30 Mar 1998	04:00
Start Cruise		17:42
Io Science objectives: full disk, n. and s. pole, eclipse, torus
Orbit 15
Start Encounter	30 May 1998	14:00
Io monitoring (NIMS/UVS)	31 May 1998	06:15
Io Closest Approach (range = 312,000)		14:00
Io eclipse (SSI)	01 Jun 1998	12:39
Io Kanehikili plume (SSI)		14:15
Io torus		19:44
Start Cruise	02 Jun 1998	11:00
Io Science objectives: surface monitoring, Kanehekili plume, high-solar phase map, eclipse, torus, surface composition, tenuous atmosphere
Orbit 16
Io Closest Approach (range = 702,000 km)	19 Jul 1998	21:55
Start Encounter		22:00
Io monitoring (PPR)	20 Jul 1998	04:30
Io torus (UVS)	21 Jul 1998	20:59
Start Cruise		14:47
Io Science objectives: monitoring, torus
Orbit 17
Start Encounter	24 Sep 1998	21:00
Io Closest Approach (range = 800,000 km)	25 Sep 1998	03:09
Io torus (UVS/EUV)	27 Sep 1998	10:55
Start Cruise	28 Sep 1998	01:30
Io Science objectives: Torus
Orbit 18
Start Encounter	21 Nov 1998	04:00
Io polarimetry (PPR)		04:49
Io surface monitoring (SSI)		23:41
Io Closest Approach (range = 996,000 km)	23 Nov 1998	03:11
Io torus (UVS/EUV)		08:29
Start Cruise		11:36
Io Science objectives: surface monitoring, polarimetry, torus
Orbit 19
Start Encounter	30 Jan 1999	18:00
Spacecraft turn for science	31 Jan 1999	09:22
Spacecraft turn for science		20:43
Io polarimetry (PPR)	01 Feb 1999	00:36
Spacecraft turn to Earth-point		04:02
Io Closest Approach (range = 856,000 km)		20:24
Start Cruise	03 Feb 1999	04:16
Io Science objectives: no entry
Orbit 20
Start Encounter	02 May 1999	10:00
Io monitoring (NIMS/UVS)		12:48
Io Closest Approach (range = 789,000 km)		12:49
Start Perijove recording (F&P)	03 May 1999	09:10
Jupiter Closest Approach (range = 669,000 km)		10:11
Io torus (EUV)	04 May 1999	09:39
Start Cruise		13:33
Io Science objectives: monitoring, composition
Orbit 21
Start Encounter	29 Jun 1999	00:00
Io Surface (UVS)		07:01
Io high resolution (SSI)	01 Jul 1999	21:04
Io global (PPR)		21:12
Io Closest Approach (range = 127,000 km)		22:08
Io spectral map (NIMS/UVS)		23:49
Io stereo w/ 124 (SSI)	02 Jul 1999	00:54
Io plume inventory (SSI)		03:58
Io torus	03 Jul 1999	03:00
Start Cruise		06:07
Io Science objectives: global composition, thermal and visual maps, plume inventory
Orbit 22
Start Encounter	11 Aug 1999	04:00
Io Closest Approach (range = 737,000 km)		07:39
Io plume inventory (SSI)	12 Aug 1999	03:59
Chorus waves (PWS)		11:00
Io torus (UVS/EUV)	13 Aug 1999	11:49
Start Cruise	14 Aug 1999	04:23
Io Science objectives: plume inventory
Orbit 23
Start Encounter	13 Sep 1999	13:00
Chorus waves (PWS)	14 Sep 1999	05:00
Start Perijove recording (F&P)		08:30
Io Closest Approach (range = 448,000 km)		14:57
Io torus (UVS/EUV)	15 Sep 1999	21:37
Start Cruise	17 Sep 1999	08:00
Io Science objectives: torus
Orbit 24 -- Details not yet worked out
Start Encounter	09 Oct 1999	20:00
Callisto Closest Approach (range = 1,220,000 km)	10 Oct 1999	01:14
Ganymede Closest Approach (range = 924,000 km)		05:06
Europa Closest Approach (range = 224,000 km)		13:44
Jupiter Closest Approach (range = 396,000 km)		19:04
Io Closest Approach (range = 2,230 km)		21:36
Start Cruise	11 Oct 1999	20:00
Io Science objectives: Features: Reiden Patera, Zammana, Hi'iaka, Gish bar, Skythia Mons, Amirani, Poliahu, Bosphorus Stereo coverage: Marduk, Dorian Mons, Prometheus, global Plumes: Pillian, Pele Plus magnetosphere
Orbit 25 -- Details not yet worked out
Callisto Closest Approach (range = 1,220,000 km)	24 Nov 1999	15:54
Start Encounter		20:00
Europa Closest Approach (range = 11,500 km)	25 Nov 1999	08:27
Jupiter Closest Approach (range = 407,000 km)		18:08
Io Closest Approach (range = 2,120 km)		20:00
Ganymede Closest Approach (range = 611,,000 km)		23:09
Start Cruise	26 Nov 1999	20:00
Io Science objectives: South pole passage Features: Prometheus plume, Malik Patera, Tupan Patera, Shamushu Patera, Zal Patera, Culann Terrains: Plateaus, giant calderas, mountains

Plans for Upcoming Orbits

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Galileo Solid State Imaging Team Leader: Dr. Michael J. S. Belton

Reference for Io pages:
A. S. McEwen et al., Active volcanism on Io as seen by Galileo SSI, Icarus 135, 181-219.

The SSI Education and Public Outreach webpages were originally created and managed by Matthew Fishburn and Elizabeth Alvarez with significant assistance from Kelly Bender, Ross Beyer, Detrick Branston, Stephanie Lyons, Eileen Ryan, and Nalin Samarasinha.

Last updated: September 17, 1999, by Matthew Fishburn

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