MEDIA RELATIONS OFFICE
CASSINI IMAGING CENTRAL LABORATORY FOR OPERATIONS (CICLOPS)
SPACE SCIENCE INSTITUTE, BOULDER, COLORADO
http://ciclops.org
media@ciclops.org

Preston Dyches (720) 974-5859
CICLOPS/Space Science Institute, Boulder, Colo.

Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

For Immediate Release: March 13, 2008

CASSINI FLIES THROUGH WATERY PLUMES OF SATURN MOON

NASA’s Cassini spacecraft performed a daring flyby of Saturn’s moon Enceladus on Wed., March 12, flying about 15 kilometers per second (32,000 mph) through icy water geyser-like jets. The spacecraft snatched up precious samples that might point to a water ocean or organics inside the little moon.

Scientists believe the geysers could provide evidence that liquid water is trapped under the icy crust of Enceladus. The geysers emanate from fractures running along the moon’s south pole, spewing out water vapor at approximately 400 meters per second (800 mph).

The new data provide a much more detailed look at the fractures that modify the surface and will give a significantly improved comparison between the geologic history of the moon’s north pole and south pole.

New images show that compared to much of the southern hemisphere on Enceladus–the south polar region in particular–the north polar region is much older and pitted with craters of various sizes. These craters are captured at different stages of disruption and alteration by tectonic activity, and probably from past heating from below. Many of the craters seem sliced by small parallel cracks that appear to be ubiquitous throughout the old cratered terrains on Enceladus.

“These new images are showing us in great detail how the moon’s north pole differs from the south, an important comparison for working out the moon’s obviously complex geological history,” said Carolyn Porco, Cassini imaging team leader, Space Science Institute, Boulder, Colo. “And the success of yesterday’s daring and very low-altitude flyby means this coming summer’s very close encounter, when we get exquisitely detailed images of the surface sources of Enceladus’ south polar jets, should be an exciting ‘next big step’ in understanding just how the jets are powered.”

This week’s flyby and another one planned for Oct. 9, 2008, were designed so that Cassini’s particle analyzers could dissect the “body” of the plume for information on the density, size, composition and speed of the particles. Among other things, scientists will use the data gathered this week to figure out whether the gases from the plume match the gases that make up the halo of particles around Enceladus. This may help determine how the plumes formed.

During Cassini’s closest approach, two instruments were collecting data–the Cosmic Dust Analyzer and the Ion and Neutral Mass Spectrometer. An unexplained software hiccup with Cassini’s Cosmic Dust Analyzer instrument prevented it from collecting any data during closest approach, although the instrument did get data before and after the approach. During the flyby, the instrument was switching between two versions of software programs. The new version was designed to increase the ability to count particle hits by several hundred hits per second. The other four fields and particles instruments on the spacecraft, in addition to the ion and neutral mass spectrometer, did capture all of their data, which will complement the overall composition studies and elucidate the unique plume environment of Enceladus.

Cassini’s instruments discovered evidence for the geyser-like jets on Enceladus in 2005, finding that the continuous eruptions of ice water create a gigantic halo of ice dust and gas around Enceladus, which helps supply material to Saturn’s E-ring.

This was the first of four Cassini flybys of Enceladus this year. During Wednesday’s flyby, the spacecraft came within 50 kilometers (30 miles) of the surface at closest approach, 200 kilometers (120 miles) while flying through the plume. Future trips may bring Cassini even closer to the surface of Enceladus. Cassini will complete its prime mission, a four-year tour of Saturn, in June. From then on, a proposed extended mission would include seven more Enceladus flybys. The next Enceladus flyby would take place in August of this year.

Images from the Enceladus flyby are available at: http://ciclops.org, http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team consists of scientists from the U.S., England, France, and Germany. The imaging operations center and team leader (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

Ronald F van Vollenhoven

Arthritis Research & Therapy 2008, 10:105doi:10.1186/ar2364
http://arthritis-research.com/content/pdf/ar2364.pdf
Published: 7 March 2008
Abstract (provisional)

In this issue of AR&T, data are presented suggesting that antirheumatic therapies decrease the risk of cardiovascular disease in patients with RA. The QUEST-RA group, a large international collaboration, analyzed data on 4363 patients in a cross-sectional manner. Traditional risk factors were all significantly associated with cardiovascular events, and the presence of extra-articular disease significantly increased the risk, confirming a previous publication. The most interesting analysis in this study suggests that effective antirheumatic treatment, with traditional DMARDs, glucocorticoids, or anti-TNF biologics, reduces the risk of cardiovascular disease in RA. However, some methodological issues are discussed, and confirmatory studies are suggested.

Patients with rheumatoid arthritis (RA) are at increased risk for cardiovascular disease. It is not yet known if antirheumatic treatments can modulate this risk in a favorable manner.

In the present issue of Arthritis Research & Therapy Naranjoand colleagues present data suggesting antirheumatic treatmentsdo modulate this increased risk [1]. The authorspresent on behalf of the QUEST-RA group, a largeinternational collaboration involving 48 rheumatologists in 15countries. Data were collected on 4,363 patients with RA in across-sectional manner, from patients and physicians byrecall and chart review. From this large dataset, the authorswere able to determine a number of facts. The patientpopulation was quite typical for established RA, and 9.3% ofthese patients reported having had cardiovascular disease orevents (heart attack and angina, coronary heart disease,coronary by-pass surgery, and stroke were included, but onlyif they occurred after RA had developed). The presence oftraditional risk factors was ascertained and, by comparingpatients with and without a cardiovascular event, most ofthese risk factors could be confirmed: higher age, male sex,hypertension, smoking (ever), diabetes, and hyperlipidemiawere all significantly associated with the risk forcardiovascular events. A more interesting finding was that thepresence of extraarticular disease clearly increased the risk ofcardiovascular events, confirming a previous publication byTuresson and colleagues [2].

The real importance of this study, however, may lie in thefinal analysis, presented in Table 5 of their paper, whichintends to determine to what extent antirheumatic treatmentmodulates the risk of cardiovascular disease [1]. To achievethis, the authors collected data from the physicians on thetreatments (glucocorticoids, conventional disease-modifyingantirheumatic drugs [DMARDs], and biologics) given to thepatients with start and stop dates. They then used theduration of treatment for each drug in each patientseparately as an independent variable in a multivariateanalysis where potential confounders were also included,including age and sex, other traditional risk factors, anddisease activity by the Disease Activity Score as well as theHealth Assessment Questionnaire disability index. Theseanalyses all show a negative relationship between the lengthof treatment with conventional DMARDs and the risk ofcardiovascular events; that is, longer duration of treatmentwith, say, methotrexate was associated with a somewhatlesser risk than a shorter duration of treatment with the sameagent. The risk reduction was quantitatively strongest withleflunomide, and was statistically significant in the moststringent analysis for all but two of the drugs under study. Asignificant but weaker relationship was also found, rathersurprisingly, with glucocorticoids, and, more in line withcurrent expectations, a stronger relationship with anti-TNFbiologics (other biologics were not assessed). The authorscautiously interpret these data as suggesting that effectiveantirheumatic treatment reduces the risk of cardiovasculardisease in patients with RA.Arthritis Research & Therapy Vol 10 No 2 van Vollenhoven

This may well be true. The current study design – aretrospective cross-sectional review based in some part onpatient recall – and using internal comparisons rather than acontrol group, however, are not ideal to address this issue. Inparticular, the use of length of treatment as the variable ofinterest raises both conceptual and technical issues. Theconceptual question is whether the length of time that apatient stays on a treatment is a good indication that thepatient had good disease control during that time. Obviouslythis is not necessarily true at the individual level, but at thegroup level this approach may work reasonably well – asdemonstrated in a number of studies, including studies ofsurvival on drugs [3,4] and a study of radiological progressionin the first 2 years of disease [5].

The technical issues are more formidable. First of all, and as theauthors themselves admit, the study is subject to leftcensoring:those patients who died of a cardiovascular eventcould obviously not contribute data. One interpretation of thestudy is therefore that antirheumatic therapy does not changethe risk of a cardiovascular event, but increases the risk that theevent will prove fatal! Obviously this is a cynical interpretation ifthere ever was one, but it may serve to underscore thedifficulties with retrospective studies. Another problem is thatthe length of each treatment is restricted by the duration of thedisease itself: those patients with the shortest disease durationat inclusion would also be more likely to contribute shortertreatment courses than those with the longer disease duration.But, importantly, this particular problem would make the resultsgo the other way, so that the criticism in fact strengthens theconclusions. A final concern worth mentioning is a channelingbias: it is conceivable that patients were given antirheumatictherapies based in part on the perception of risks associatedwith these agents for that particular patient, and cardiovascularrisk factors might have played in that decision. An examplewould be that leflunomide would be chosen less often forpatients with hypertension, or that glucocorticoids would beavoided in patients with diabetes. When the authors controlledfor these known risk factors, however, the association betweentreatment and risk was generally maintained.

Taking these data at face value, it is quite striking that almostall of the antirheumatic therapies investigated provided abenefit. This would strongly argue against a specificpharmacologic effect separate from the antirheumatic effect,but rather supports the idea that this efficacy is conveyed bydecreasing the immune-mediated inflammatory processunderlying atherogenesis [6] and/or plaque instability [7].

The final message of Naranjo and colleagues’ paper, and onethat should be encouraging to those of us managing patients,is that our insistence on the sustained use of appropriateantirheumatic therapies, while not always the most popularwith patients, has been the right approach all along – not onlywith a view on the rheumatic disease itself, but also for thecardiovascular complications.In summary, the possibility that antirheumatic therapydecreases the risk for cardiovascular complications istantalizing. The current study, while not exactly proving thispoint, adds a further measure of support to the concept, andsuggests that it must now be formally addressed, either by arigorously designed and implemented prospective cohortapproach or by a controlled clinical trial.

Competing interests

The author declares that they have no competing interests.