Virgil Adumitroaie

Jupiter’s interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft

Juno swoops around giant Jupiter Jupiter is the largest and most massive planet in our solar system. NASAs Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Junos flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiters aurorae and plasma environment, both as Juno approached the planet and during its first close orbit. Science, this issue p. 821, p. 826 Juno’s first close pass over Jupiter provides answers and fresh questions about the giant planet. On 27 August 2016, the Juno spacecraft acquired science observations of Jupiter, passing less than 5000 kilometers above the equatorial cloud tops. Images of Jupiter’s poles show a chaotic scene, unlike Saturn’s poles. Microwave sounding reveals weather features at pressures deeper than 100 bars, dominated by an ammonia-rich, narrow low-latitude plume resembling a deeper, wider version of Earth’s Hadley cell. Near-infrared mapping reveals the relative humidity within prominent downwelling regions. Juno’s measured gravity field differs substantially from the last available estimate and is one order of magnitude more precise. This has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter’s core. The observed magnetic field exhibits smaller spatial variations than expected, indicative of a rich harmonic content.

The distribution of ammonia on Jupiter from a preliminary inversion of Juno Microwave Radiometer data

The Juno microwave radiometer measured the thermal emission from Jupiters atmosphere from the cloud tops at about 1 bar to as deep as a hundred bars of pressure during its first flyby over Jupiter (PJ1). The nadir brightness temperatures show that the Equatorial Zone is likely to be an ideal adiabat, which allows a determination of the deep ammonia abundance in the range 362^(+33)_(-33) ppm. The combination of Markov chain Monte Carlo method and Tikhonov regularization is studied to invert Jupiters global ammonia distribution assuming a prescribed temperature profile. The result shows (1) that ammonia is depleted globally down to 50–60 bars except within a few degrees of the equator, (2) the North Equatorial Belt is more depleted in ammonia than elsewhere, and (3) the ammonia concentration shows a slight inversion starting from about 7 bars to 2 bars. These results are robust regardless of the choice of water abundance.

Capability Investment Strategy to Enable JPL Future Space Missions

The Jet Propulsion Laboratory (JPL) formulates and conducts deep space missions for NASA (the National Aeronautics and Space Administration). The Chief Technologist of JPL has responsibility for strategic planning of the laboratory’s advanced technology program to assure that the required technological capabilities to enable future missions are ready as needed. The responsibilities include development of a Strategic Plan (Antonsson, E., 2005). As part of the planning effort, a structured approach to technology prioritization, based upon the work of the START (Strategic Assessment of Risk and Technology) (Weisbin, C.R., 2004) team, was developed. The purpose of this paper is to describe this approach and present its current status relative to the JPL technology investment strategy. The JPL Strategic Technology Plan divides the required technological capabilities into 13 themes. The results reported here represent the initial analysis of seven themes: In-situ Planetary Exploration Systems, Survivable Systems for Extreme Environments, Precision Flying Systems, Deep Space Communication, Planetary Protection Systems, Utilization of High Capability Computing, and Engineering Systems. The remaining six themes will be included in the study planned for FY ’06. Each theme is hierarchically decomposed into component capabilities, to a level where quantitative estimates can be ascribed. For example, in the In-Situ Exploration theme, the sub-theme of Mobility is broken down into Surface Mobility, which allows an estimate of the meters traversed per command, a specific and measurable quantity. This structure is repeated and data filled in for each mission. All of this information is analyzed using an optimization technique (Martello, S., 1990) formulated to maximize total missions technologically enabled subject to overall cost constraints. Note that capabilities are given credit only if all capabilities needed to enable a particular mission are selected for funding. The recommended investments at each area of the capability hierarchy are plotted as a function of the total budget available to the sponsor. The robustness of the investment strategy is quantitatively analyzed as a function of potential variation (the uncertainty) of the input data. In on-going work we are looking at measures for relative mission value, dependencies among missions and capability areas, and time profiles of the recommended investments.

Prevalent lightning sferics at 600 megahertz near Jupiter’s poles

Lightning has been detected on Jupiter by all visiting spacecraft through night-side optical imaging and whistler (lightning-generated radio waves) signatures1–6. Jovian lightning is thought to be generated in the mixed-phase (liquid–ice) region of convective water clouds through a charge-separation process between condensed liquid water and water-ice particles, similar to that of terrestrial (cloud-to-cloud) lightning7–9. Unlike terrestrial lightning, which emits broadly over the radio spectrum up to gigahertz frequencies10,11, lightning on Jupiter has been detected only at kilohertz frequencies, despite a search for signals in the megahertz range12. Strong ionospheric attenuation or a lightning discharge much slower than that on Earth have been suggested as possible explanations for this discrepancy13,14. Here we report observations of Jovian lightning sferics (broadband electromagnetic impulses) at 600 megahertz from the Microwave Radiometer15 onboard the Juno spacecraft. These detections imply that Jovian lightning discharges are not distinct from terrestrial lightning, as previously thought. In the first eight orbits of Juno, we detected 377 lightning sferics from pole to pole. We found lightning to be prevalent in the polar regions, absent near the equator, and most frequent in the northern hemisphere, at latitudes higher than 40 degrees north. Because the distribution of lightning is a proxy for moist convective activity, which is thought to be an important source of outward energy transport from the interior of the planet16,17, increased convection towards the poles could indicate an outward internal heat flux that is preferentially weighted towards the poles9,16,18. The distribution of moist convection is important for understanding the composition, general circulation and energy transport on Jupiter.Observations of broadband emission from lightning on Jupiter at 600 megahertz show a lightning discharge mechanism similar to that of terrestrial lightning and indicate increased moist convection near Jupiter’s poles.

Implications of the ammonia distribution on Jupiter from 1 to 100 bars as measured by the Juno microwave radiometer

The latitude-altitude map of ammonia mixing ratio shows an ammonia-rich zone at 0-5°N, with mixing ratios of 320-340 ppm, extending from 40-60 bars up to the ammonia cloud base at 0.7 bars. Ammonia-poor air occupies a belt from 5-20°N. We argue that downdrafts as well as updrafts are needed in the 0-5°N zone to balance the upward ammonia flux. Outside the 0-20°N region, the belt-zone signature is weaker. At latitudes out to ±40°, there is an ammonia-rich layer from cloud base down to 2 bars which we argue is caused by falling precipitation. Below, there is an ammonia-poor layer with a minimum at 6 bars. Unanswered questions include how the ammonia-poor layer is maintained, why the belt-zone structure is barely evident in the ammonia distribution outside 0-20°N, and how the internal heat is transported through the ammonia-poor layer to the ammonia cloud base.

Analysis of Concepts for Large-Scale Robotic Lunar Precursor Missions

Two concepts for large-scale, complex, robotic missions to search for frozen water at the lunar South Pole are systematically analyzed to determine their relative productivity and investment requirements. The Strategic Assessment of Risk and Technology (START) methodology and tool are utilized to determine temporal R&D-investment recommendations to optimize mission performance goals subject to budget, workforce, and other non-technical constraints. Explicit distinction is made between enabling and enhancing technologies. Uncertainties and dependencies are included within the optimization framework. This study determined that given the constraints used in this analysis, the longer mission would return 12 times the value of the shorter mission for roughly an 11% increase in cost, and would be enabled with the recommended temporal technology portfolio.

Capability development return on investment for the NASA aeronautics program

As part of a multi-agency effort to improve Americas air transportation system, NASA has undertaken a study to develop and demonstrate a systematic method for selecting capability investments based on their projected return on investment.

First look at Jupiter's synchrotron emission from Juno's perspective

Since August 2016, measurements of Jupiters microwave emissions at six wavelengths ranging from 1.3 cm to 50 cm have been made with the Juno Microwave Radiometer (MWR). In this paper, we introduce the first systematic set of in-situ observations of synchrotron radiation in a polar plane while describing the modeling approach we use to analyze this data (collected August 27th, 2016). Time series of brightness profiles at all six frequencies present similarities that are explained by the presence of known regions of intense synchrotron radiation. Our model predictions, though limited for now to the total intensity of the radiation, reproduce (qualitatively) the observation of temporal variations and allow to disentangle the synchrotron emission from the atmospheric emission. The discrepancies seen between the data and simulations confirm that physical conditions close to Jupiter affecting synchrotron emission (electron energy spectra, pitch-angle distributions, and the magnetic environment) are different than we anticipated.

Towards a fast background radiation subtraction technique for the Juno mission

The Juno spacecraft will go into polar orbit after it arrives at Jupiter in 2016. Scientific instruments on Juno will make in situ charged particles and magnetic fields measurements. Remote sensing instruments will measure thermal and non-thermal emissions from the atmosphere and magnetosphere. Gravitational field measurements will be derived using radio tracking signals. The Microwave Radiometer (MWR) Instrument, one of the nine instruments on Juno, has been designed to measure the brightness temperatures of Jupiter at six microwave frequencies, sounding the atmosphere from 0.5 atm to over 100 atm pressure. Synchrotron emission generated by ultra-relativistic electrons trapped in Jupiters magnetosphere will be detected and measured by the MWR Radiometer over a range of wavelengths from 2 cm to 50 cm. Synchrotron data collected with the MWR Radiometer will be used for two purposes: a) to improve the atmospheric measurements, and b) to provide new constraints on the synchrotron emission itself. The ancillary MWR data analysis requires a fast synchrotron radiation model that can be used in conjunction with the atmospheric retrieval algorithm. This paper describes an extension of the Levin at al. (2001) multi-zonal, multi-parameter model to a spacecraft point of view, along with a few testing and validation cases.

Comparison of Lunar Surface Mission Productivities as a Function of Mission Duration and Weighted Science Objectives

We formulate, model and analyze two proposed missions near the lunar south pole of different durations and scientific emphasis. Each mission is conducted by two teams of two astronauts riding in two pressurized rovers. Each team must remain within the same locality as the other team in case there is need for a rescue. Our analytical approach combines the best features of two analytic techniques, SciMax and HURON, to overcome difficulties of combinatorial explosiveness of the trade space, and to enable scheduling of “as much science as possible” rather than an inflexible set of experiments that may not make optimal use of available time. Weighting of individual science goals leads to different sets of scientific investigations and different amounts of time to be spent at the various sites. We demonstrate that increased rover driving speeds increases the amount of time available to spend at sites, and thus increases science productivity dramatically up to a point. Beyond that point, increasing driving speed improves productivity marginally due to the lack of availability of EVA time.